Museum of Comparative Zoology HERPETOLOGY LIBRARY Ernst Mayr Library "^ I ) ■ i -> MuseuiTi of Comparative Zoolcgy Harvard University / O 3T-JM-.«Mi-^ t oJ^ftr\x» A HISTORY OF BRITISH FOSSIL REPTILES. BY Sill EICIIARD OWEN, K.C.B., E.R.S., Etc., FOEEIQN ASSOCIATE OF THE INSTITUTE OF FEANCE (ACADEMY OF SCIENCES). VOL. I. LONDON : CASSELL & COMPANY LIMITED, LA BELLE SAUVAGE YAKD. 1849—84. PUINTEil BY J. E. ADLAED, BAETIIOLOMEW CLOSE. This Work was on'p-hial/v issued ERRATA. Vol. I., p. 200. — The genus Polypiycliodon was found to belong to the order Saicropterygia : see p. 455. fi. p. 213. — The marine reptiles associated under the term Enaliosaitria were subsequently divided, as the number of discovered species increased, into the orders Ichlhyoptefjgia and Sauropterygia: see Vol. III., pp. I and 41. lb. p. 405. — The genus Cetiosaiwus was shown to belong to the order Dinosauria : see p. 577. lb. p. 426. — The suggestion at the foot of this page received the con- firmation given in p. 627. in Parts, by private ion of the Fossil ers of new species 'imens, led me to ■Is for the present ubinit them to the ich cannot be re- Six Parts pre- tlie IVoric uiill be to the Publishers. ^ /(J-L /y^ No. of this copy PEEFACE. At the date of the last (posthumous) edition of Cuvier's ' Rechcrches sur les Ossemens Fossiles,'^ descriptions and figures were given of a few fossil Crocodiles, to two Oolitic species of which Geoffroy St. Hilaire had given the generic names of Teleosaunis and Steneosaurus. To these follow descriptions of certain Tertiary Fossils of the order Chelonia, referable to the genera Testudo, Emys, Trlonyx, and, by a Cretaceous form, to the genus Ghelone. To the order Lacertilia Cuvier refers the gigantic extinct Reptile from the Maestricht Chalk, since termed Mosasaurus, and the genus from secondary marls near Monheim to which he assigns the name Geosaurus, not intimating thereby that the species was exclusively terrestrial, but " par allusion a la terre mere des geans" (p. 184, t. x.). Cuvier then gives a summary of Buckland's discovery and description of the remains from the Oxford Oolite, referred to the genus Megalosmirus, "quiparait tenir des Sauriens et des Crocodiles " (p. 185) ; also of Mantell's discovery of fossils from the Weald of Sussex which, after Cuvier's opinion on the dental character, were referred to the genus Iguanodon. Cuvier then proceeds to the description of Collins's and Soemmering's fossils of a volant animal which was determined by Cuvier to be those of a Reptile, and for which he proposes the name Pterodactylus. At that date no evidences of this genus had been recognised in secondary or other formations of Britain. The descriptions and inferences occupying pp. 215, 261, of the concluding volume of the ' Ossemens Fossiles ' are models of palfBonto- graphical work. Cuvier finally translates, with original remarks, the descriptions by Home and de la Beche of the Ichthyosaurus, and those by Conybeare of the Plesiosaurus ; the letterpress figures being limited to a single species of each of these Liassic genera. In conclusion, the immortal Founder of Palseontological Science, writes : — " J'avais aussi le projet de donner des chapitres sur les os d'oiseaux et de serpens ; mais — j'ai du renoncer a cette partie de mon plan " (tome dixieme, p. 475). 1 8vo, 10 volumes, edited by M. Feedebic Cuvieb, 1834 — 1836. ii PREFACE. After referring to the localities in which the remains attributed to birds (as those by Buckland from the Oolitic Slate of Oxford) had been found, Cuvier proceeds : — " Les os de serpens sont encore plus rares, s'il est possible. Je n'en ai vu que des vertebres des breches osseuses de Cette, et une seule des terrains d'eau douce de I'lle de Sheppey " (ib., p. 476). My determination of the Fossil Remains collected by John Hunter and described in the ' Catalogues of the Hunterian Collections ' then under my charge, together with the knowledge of other fossil remains of Reptilia with which holiday geological excursions and the transmissions by local collectors had made me acquainted, begat a conviction that the contributions of Buckland, De la Beche, Conybeare, and Mantell, were but the forerunners of other, probably much more extensive, acquisitions of evidences of Reptilian modifications of vertebral struc- tures from British strata. The application of a grant by the " British Association for the Advancement of Science," in aid of such research, enabled me to visit and personally explore the most promising localities of Reptilian Fossils, the results of which were communicated in two " Reports," published in the ' Transactions of the Association ' for the years 1841 and 1842. The foundation of the " Pal^ontographical Society," in which I co-operated with BowERBANK, Thomas Bell, and Searles Wood, gave subsequent opportunities of putting on record the characters of species of British Fossil Reptiles, at that time new to science. The contribution of such descriptions to the annual volumes was attended with the Society's permission to take, at my own cost, impressions of the plates, after their use by the Society, for the pui'pose of the present work. Its issue in " Parts " exhausted the materials at my command in 1854, and I thought that the new Fossil Reptiles, of which I received indications, would occupy a concluding part of like size and number of plates with its forerunners. But the acquisitions of fragmentary fossils, suggestive of new species or genera of Beptilia, beguiled me into procrastinating hopes of reconstructions which, in some instances have been fulfilled. In the excitement of such quests after draconic forms time passes swiftly, and conviction becomes imperative that it must have a term. Moreover, a Record of what may have been discovered of a given group or class of Natural Objects, especially of Fossil Remains, with figures aiding recognition and comparison, becomes a help and stimulus to rapid and extensive additions. The attempt to grapple with these and make them usefully known has absorbed year liy year such leisure as I could so devote after oflicial duties. The result is summarised in the Indexes to Volumes I and III of the present work. PREFACE. iii Another benefit flows from publication ; the correction, viz. of errors into which the author may have fallen. His acceptance, for example, of Mantell's and Cuvier's determinations of parts of the Iguanodon as the " tympanic bone '' and " clavicle " has been rectified ; in regard to the first, by the accomplished Professoi- Seeley's recognition of it as part of a vertebra of another genus and species ; and, in regard to the second, by Professor Leidy's reference of it to a part of the pelvis, as a pubic bone. The more recent discovery, in a Belgian locality, of an almost entire skeleton of an Iguanodon confirms these rectifications, and almost completes the restoration of that truly remarkable gigantic extinct form of phytophagous Reptile.' And here I cannot but gratefully notice the truly valuable additions to our knowledge of Dinosaui'ian fossils made by the personal labours, enterprise, and science of Professor 0. C. M.arsh, of Yale College, New Haven, Connecticut, United States. Such indications of the numbers of animal forms, which have existed during long epochs of our earth's past histoi'y, give an impression that the labours of an individual devoted to the fossil remains of a limited group can but leave a mere sketch of a fragment of the class — a sketch, however, which cannot fail to be filled in by the labours of successive generations of Palgeontologists. ^ These remains were discovered, in 1881, at Bernis.'sart, and their matrix was determined bv the accomplished Director of the Eoyal Museum of Natural History, Brussels, Prof. Edouaru Dupont, to belong to the Wealden Series ; the fossils are referred by Prof. P. G. Van Beneden to belong to the species Iffuanodon Mantelli. (' Bulletin de I'Academie Eoyale des Sciences de Belgique,' 8vo, 1881, p. GUO.) CONTENTS. PAGEINDEX. SECTION I. FOSSIL REPTILIA OF THE TERTIAUY FORMATIONS. Order— CHELONIA. § 1 • Structure and Homologies of the Carapace and Plastron § 2. Family — Marina. Genus — Chelone Species — Chelone breviceps . — longiceps . — latiscutata — convexa — subcristata — planimentum — crassicostata — declivis — trigoniceps — cuneiceps . — subcarinata Supplemental remarks on the species from Harwich Summary on the genus Chelone § 3. Family — Fluvialia. Genus — Trionyx . Species — Trionyx Henrici — BarbarcB . — incrassatus — marginatus — rivosus — planus — eircumsulcatus — pustulatus PAGE 1 7 10 16 20 21 24 25 27 30 31 33 37 40 44 45 46 50 51 55 56 58 59 60 VI PAGE-INDEX. § 4. — Family — V(tludinosa Genus — Platemys Species — Platemys BiiUockii — Bowerbankii Genus — Emys Species — Emys testudiniformis — leevis — Comjitoni — bicarinata — Delabecliii — crassus Platemys Boiverbankii ? PAGE 61 62 62 66 67 67 70 71 73 74 76 77 Order— CROCODILIA. Osteological Characters § 5. Genus — Ckocodiltjs. Species — Crocodilus toliapiciia — champsoides — Hastingsii § 6. Genus — Alligator Species — Alligator Hantoniensis § 7. Genus— Gavialis Species — Oavialis Dixoni . 80 112 115 120 126 126 129 129 Order— LACERTILIA. § 8. Genus — Lacerta Species — Lacerta eocena 133 133 Order— OPHIDIA. §9- § 10. Genus— Pal^ophis 139 Species — Palceophis typhceus — porcatus 139 144 — toliapicus — lonffus . Genus — Paleryx 146 149 149 Species — Paleryx rhombifer — depressus 150 150 PAGE-INDEX. vu SECTION II. EOSSIL EEPTILIA OE THE CRETACEOUS EOEMATIONS. CHAPTER I. Order— CHELONIA. § 1. Genus— Chelone Species — Chelone Benstedi . — pulchrieeps ■ — Camperi . — indeterminata § 2. Genus — Pkotemys Species — Protemys serrata . PA6B 155 158 162 163 166 169 169 CHAPTER II. Order— LACERTILIA. Tribe — Repentia 173 §4. Genus— Rapkiosaukus Species. — Rapkiosaurus subulidens 173 173 §i- Genus— CoNiosAURUS Species — Coniosaiirus crassidens 175 175 §6. Genus — Dolichosaurus Species — Dolichosaurus longicollis Tribe — Natantia 176 176 183 §7. Genus — Mosasaueus Species — Mosasaurus gracilis 183 . 185 §8. Genus — Leiodon Species — Leiodon anceps . 195 . 196 CHAPTER III. Order— CROCODILIA. § 9. Genus — Crocodiltjs Species — Saulii . § 10. Genus — Polypttchouon Species — Polyptychodon continuus — Mackesoni — inlerruptus 199 199 200 201 201 201 X Vlll PAGE-INDEX. CHAPTER IV. Order— EN ALOSAURIA. § II. Genus — Plesiosaxjrus Species — Plesiosaurus Bernardi — constrictus — Smithii — pachjnmus § 12. Genus — Ichthyosaurus Species — Ichthyosaurus campylodon PAGE 213 214 215 217 218 222 223 CHAPTER V. Order— PTEROSAURIA. § 13. Genus — Ptehodactylus Species^ — Pterodactylus Cuvieri — giganteus (conirostris) — eompressirostris 234 242 245 249 14. CHAPTER VI. Ordkr— DINOSAURIA. Genus — Iguaxodon . . . . Species — MantelU . . . . Concluding Remarks on Tertiary and Cretaceous Reptilia 259 266 272 SECTION III. FOSSIL EEPTILIA OE THE WEALDEN EOEMATIONS. CHAPTER I. Order- DINOSAURIA. § 1. Genus — Iguanodon Species — Iguanodon Mantelli § 2. Genus — Megalosaurus Species — Megalosaurus Bucldandii 275, 373 . 276 . 329 . 332 PAGE-INDEX. IX §3. §4. §5. Genus — HYLJiOSAURUS .... Species — Hylceosaurus armatus Genus — Iguanodon (Supplement No. I) Restoration of the hind foot (Section II, Scpplement No. 1.) Cretaceous Pterodactyles Order— PTEROSAURIA. Genus — Ptekodacttlus .... Species — Pterodactylus Sedgwickii — Fittoni page 355 358 373 373 379 379 379 381 §6. §7. §8. §9- § 10. § 11- § 12. CHAPTER II. Order— CROCODILIA. Genus — Streptospondylus Species^ — Streptospondylus major Genus — Cetiosaueus Species — Cetiosaurus brevis Genus — Pelorosaurus Species — Pelorosaurus Conyhearii Tootli of Cetio- or Poloro-saurus Genus — Poikilopleuron . Species — Poikilopleuron Bucklandii Genus — Goxiopholis Species — Goniopholis crassidens Genus — ^SUCHOSAUEUS Species — Suchosaurus cultridens (Section II, Supplement No Cretaceous Pterodactyles Genus — Pterodactylus Species — Pterodactylus sitnus — Woodwardi (Section II, Supplement No Cretaceous Enaliosaurs . 2.) 1.) Order— SAUROPTERYGIA. § 13. Genus — Polyptychodon . Species — Polyptychodon interruptus . 398 399 405 405 414 416 420 422 426 427 427 433 433 436 436 437 439 455 455 455 PAGE-INDEX. § 14 § 15. (Section II, Supplement No. 1.) Cretaceous Lizahds Tribe — Natantia Genus — Leiodon Species — Leiodon anceps (Section II, Supplement No. 3.) LiASSic Ptehodactyles Genus — Dimorphodon Species — Bimorphodon maeronyx PAGK 460 460 460 463 463 467 SECTION III {continued). § 16. Genus- — Iguanodon .... . Species — Iguanodon Mantelli (Bones of Forearm and Paw) — Foxii .... § 17. Genus — Hyl^ochampsa .... Species — HyltBochampsa vectiana 503 503 520 531 531 SECTION IV. MESOZOIC REPTILIA. Order— PTEROSAURIA. §1. Genus — Pterodactylus Species — Pterodactylus Baviesii — sagittirostris . 537 . 537 . 538 §2. Genus — Goloborhynchus . Species — Goloborhynchus clavirostris Pterodactylus Mansclii — Pleydellii — incertus — Kiddii — Buncani — Aclandi — Marderi . 542 . 542 . 544 . 544 . 544 . 546 . 545 . 545 . .548 Order— DINOSAURIA. § 3. Genus — Bothriospondylus Species — Bothriospondylus su_^ossiis 551 551 PAGE-INDEX. XI § 4. Genus — Omosaurus Species — Omosaurus armatus § 5, Genus — Cetiosaueus Species — Cetiosaurus longus § 6. Life and kinship of Dinosaurs Carpal spine of Omosaurus . § 7. Genus — Chondrosteosaurus Species — Chondrosteosaurus gigas Genus — Cardiodon Species — Cardiodon rugulosus § 8. Genus — Poikilopleuron Species — Poikilopleuron pusillus PAGE 556 556 577 577 595 620 622 622 625 625 , 627 , 628 Order— CROCODILIA. §9- Genus — Goniopholis Species — Goniopholis sitmts . — tenuidens 631 631 642 § 10. Genus — Petrosuchus Species — Petrosuchus leevidens 634 634 § 11. Life and kinship of Crocodilia 636 § 12. Genus — Bracuydecxes Species — Brachydectes major — minor 643 643 644 § 13. Genus — Nannosuchus 646 § 14. Species — Nannosuchus gracilidens Genus — Theriosuchus Species — Theriosuchus pusillus 646 650 650 Order— LACERTILIA. § 15. Genus — Ncthetes Species — Nuthetes destructor Dermal bones (or "granicones ") 655 655 656 CONTENTS. SYSTEM-INDEX. Order— CHELONIA. Family — Marina (turtles). PAGE Genus — Chelone ...... 7 — 155 Species — Chelone breviceps . . 10 — lonyiceps . . 16 — latiscutata . 20 — convexa subcristata . 21 . 24 — planimentum ' 25, 40 — crassicostata 27,42 — declicis . 30 — triyoniceps 31 — cuneiceps . . 33 — subcarinata . 37 — Banstedi . . 158 — pulchriceps . 162 — Camperi . . 163 Family — Fluvialia (soft turtles). Genus — Tbionyx . . . . . • .45 Species — Triony X Henrici . . 46 — Barbaree . . 50 — incrassatus . 51 — marginatns . 55 — rivosus 56 — planus . 58 — circumsulcatus . 59 — pnatulatus . 60 Family — Patud '.nosa (terrapenes or freshwater tortoises). Genus — Emys • 67 Species — Emys testudinifoiTnis . • • • • .67 Irevis . 70 SYSTEM-INDEX. XIII page Species — Emys Comptoni .... . 71 — bicarinata .... 73 — Belabechii .... . 74 — crassits .... 7(i Genus — Platemys .... . 62 Species — Platemys Bullockii . 62 — Bowei-bankii 66,77 Genus — Protemys .... . 169 Species — Protemys serrata .... . 169 Order— LACERTILIA. Tribe — Repentia .... 133—173 Genus — Lacerta .... . 133 Species — Lacerta eocena .... . 133 Genus — Raphiosackus .... . 173 Species — Raphiosaurus subulidens . 173 Genus — Coniosaueus .... . 175 Species — Coniosaurus crassidens . 175 Genus — Dolichosaurus .... . 176 Species — Dolichosaurus longicollis . 176 Genus — NUTHETES .... . 655 Species — Nnthetes destructor . 655 Tribe — Natantia .... . 183 Genus — Mosasaurus .... . 183 Species — Mosasaurus gracilis . 185 Genus — Leiodon ..... . 195 Species — Leiodon anceps .... 196,460 Order— OPHIDIA. Genus — Pal^eophis .... . 139 Species — Paleeophis typkcBus . 139 — purcatus . 144 — toliapicns . 146 — longus .... . 149 Genus — Paleeyx .... . 149 Species — Paleryx rhombifer . 150 — depressus .... . 150 Order— CROCODILIA. Genus — Crocodilus Species^ — Crocodilus toliapicns — champsoides — Hastingsies Genus — Alligator Species — Alligator hantoniensis Genus — Gavialis 112 112 115 120 126 126 129 XIV SYSTEM-INDEX. Species- Geuus — Species- Genus— Species- Genus— Species Genus— Species- Genus— Species- Genus— Species- Genus— Species- Genus- Species- Genus— Species- Genus— Species- Genus— Species- Genus— Species- Genus— Species Genus— Species- Genus— Species- Genus— Species- Geuus- Species Genus- -Gavialis Dixoni . Stkeptospondylus —Streptospondylus major -GONIOPHOLIS -Goniopholis crassidens — simus . — tenuidens •SUCHOSAURUS —Suchosaurus cultridens -Hyl,«ochampsa —HylcBOchampsa vectiana -Petrostjchus -Petruauchus Icevidens Brachydectes —Brachydectes major — tninor -Nannosuchus —Nannosuchus gracilidens -Theeiosucuus —Theriosuchus pusillus Order— DINOSAURIA ■Cetiosaukus — Ceiiosaurus brevis lungus -BOTHKIOSPONDYLUS —Buthriospondylus svffossus — longus — magnus -Chon'drosteosaukus — Chondrosfeosaurus gigas -Omosaurus — Omosaurus armatus — hastiger -Cardiouon — Cardiodon rvgulosus -Pelorosaurus — Pelorosaurus Conybearii -Htl^osaurus — Hylceosaurus armatus -Poikilopleuron . —Poikiiopleuron BucMandii — pusillus -Megalosaurus — Megalosaurus BucMandii -Iguanodon PAGE 129 398 399 427 427 631 642 433 433 531 531 634 634 643 643 644 646 646 650 650 405,577 . 405 . 579 . 551 . 551 . 657 . 658 . 022 . 622 . 556 . 556 . 620 . 625 . 625 . 414 416, 420 . 355 355—358 . 422 422—426 . 628 . 329 329—354 . 275 SYSTEM-INDEX. XV Species— Iff uanodon Mantelli — — (restoration ofhiiul foot) — — (restoration of fore foot) — Foxii (restoration of skull) Order— PTEROS AURI A Genus — Pterodactylus Species — Pterodactylus Cttvieri — conirostris — compressirostris — Sedgwickii — Fittoni — simus Woodwardii — Baviesii suyittirostris — Manselii — Pleifdellii — Kiddii — Duncani — Aclandi — Marderi Genus — Coloborhynchus . Species— Coloborhy7ichus davirostris Genus — CiiioKHYNCHUs Species — Criorhynchm simus Genus — DijiorphodOxN Species — Dinwrphodon macronyx PARE 27«— 328 . 373 . .i03 . 520 . 234 . 242 . 245 . 249 . 379 . 381 . 437 439—454 . 537 . 538 . 544 . 544 . 54ti . 547 . 547 . 548 . 542 . 542 437—550 437—550 . 463 4(i7, 548 Order— EN ALIOSAURIA. Sub-order — Sauropterygia. Genus — Plesiosaurus Species — Plesiosaurus Bernardi — ■ constrictus — Smithii — pachyomus Genus— PoLYPTYCHODON Specks— Polyptychodon continuus — interrnptus Sub-order — Ichthyoptkrygia . Genus — Ichthyosaurus Species — Ichthyosaurus campylodon • 213 214 215 217 220 . 218 200, 455 . 201 209 222 223 A HISTOEY OF BRITISH FOSSIL REPTILES. CHAPTER I.— Order CHELONIJ. TURTLES, TERRAPENES, AND TORTOISES. ^ 1. Introdadory BeDiarks on the Ilomolor/i/ of ihe Carapace and Plastron. The majority of the Fossil Chelonians, defined or descril^ed in my ' Report on British Fossil Reptiles,'* belonged to the marine division of the order, and as the species of this family depart least from the ordinary reptilian type in the modification of the -bones of the trunk, composing the characteristic thoracic-abdominal case of the order, I propose to commence with them the descriptions of the Fossil Reptilia which form the subject of the present Chapter. In order to facilitate the comprehension of the descriptions and figures of the fossil Chelonians, a brief notice is premised of the composition and homologies of the carapace and plastron, or roof and floor, of that singular portable abode, with which the reptiles of the present order have been endowed in compensation for their inferior powers of locomotion or other modes of escape or defence. In the marine species of the Chelonian order, of which the Chelone nujdas may be regarded as the type, the ossification of the carapace and plastron is less complete, and the whole skeleton is lighter than in those species that live and move on dry land: but the head is proportionally larger — a character common to aquatic animals, — and being incapable of retraction within the carapace, ossification extends in the direction of the fascia, covering the temporal muscles, and forms a second bony covering of the cranial cavity ; it is interesting to observe, however, that this accessory defence is not formed by the intercalation of any new bones, but is due to exogenous growth from the frontals (ii), parietal (7), postfrontals (12), and mastoids (s, see Pis. 1 1, and MA). The bony carapace is composed externally of a series of median and symmetrical pieces (fig. 1, cJi, f<\—s\\, pij), and of two series of unsymmetrical pieces (phs, m\ — 12) on each side. The median pieces have been regarded as lateral expansions of the summits of the upper vertebral (neural) spines,! the median lateral pieces as similar * Reports of the British Association for the Advancement of Science, 1841, p. \CM. t Cuvier, Lemons d'Anatomie Comparee, torn, i (1799), p. 212. B 2 BRITISH FOSSIL REPTILES. developments of the vertebral ribs (pleurapophyses),* and the marginal pieces as the homologues of the sternal ribs (h£emapophyses).t I must refer the reader to my Memoir, communicated to the Royal Society, Jan. 1 8, 1849, for the facts and arguments which have led me to regard these pieces, as dermal ossifications, homologous with those that supjjort the nuchal and dorsal epidermal scutes in the crocodile. Most of the bony pieces of the carapace are, however, directly con- tinuous, and connate, J with the obvious elements of the vertebrae, which have been supposed exclusively to form them by their unusual development ; the median pieces have accordingly been called " vertebral plates," and the medio-lateral pieces " costal plates." I retain the latter name, although with the understanding and conviction that they are essentially or homologically distinct parts from the vertebral ribs or pleurapophyses with which they are connate and more or less blended. But, with regard to the term " vertebral" plate, since the ribs {costaf) are as essentially elements of the vertebrse as the spinous processes themselves, I have been in the habit, in my Lectures, of indicating the median series by the term " neural plates," which term has the further advantage of removing any ambiguity from the descriptions that might arise from their being mistaken for the superincumbent epidermal shields, which are likewise called " vertebral plates" in some English works. § The term " marginal" is retained for the osseous plates forming the periphery of the carapace ; but the median and symmetrical ones, which seem also to begin and end the " neural" series, are specified, the one by the term " nuchal plate," the other by that of " pygal plate." The " neural plates" are numbered as in the classical Monograph of Bojanus.|| In the subjoined woodcut of the carapace of the loggerhead turtle {Chelone caouanna) (fig. 1), ch is the nuchal plate ; si to si l the neural piafes ; jjIi topis the costal plates ; and m 1 to m 1 2 the marginal plates. The carapace is impressed by the superimposed epideiTnal scutes or shields, which consist of a median series, called " vertebral scutes" v\ to vb ; * Ibid. p. 211. Rathke has recently supported this determination by arguments drawn from the mode of development of the carapace. See ' Annales des Sciences Naturelles,' Mars, 1S4G ; and ' Ueber die Entwickelung der Schildkroten,' -Jto, 1848, where he says, p. 10.5 : — " Ausser den Rippen und den horizontal liegendeu Tafein, zu welchen sich die Dornfortsiitze des zweiten uiul der sechs folgendeu Riiekenwirbel aasbilden, dienen bei den erwachsenen Schildkroten zur Zusammeusetzung des Riickenschildes noch eine oder mehrere Knochenplatten," viz. the "marginal plates." I have shown how Rathk6 was deceived by over-estimating the character of connation, in my ' Observations on the Development of the Carapace and Plastron of the Chelonians,' which conduct to a diiferent conclusion to that at which Cuvier and Rathke have arrived. (Philosoph. Transactions, IB^'J.) f GeofTroy, Annales du Museum, tom. xiv (1809) p. 7. X This term is used in the definite sense explained in my work on the '.\rchetype of the Vertebrate Skeleton' (8vo, V. Voorst, p. 49), as signifying those essentially different parts which are not physically distinct at any stage of development ; and in contradistinction to the term " confluent," which applies to those united parts which were originally distinct. § See Grifliths's translation of Cuvier, vol. ix, Synopsis of Regtilia, p. G — " fifth vertebral plates prominent." [| Anatome Testudinis Europceee, fol. 1821, tab. iii and iv. CHELONIA. Fie:. 1. Carapace of the Loggcrlicad Turtle (Chelone cuouamui). and of a lateral series of " costal scutes " there is also a peripheral series of " marginal scutes'" corresponding with and impressing the mar- ginal plates. The nuchal ])late [cJi) is remarkable for its breadth in all Chelonia, and usually sends down a ridge from the middle line of its under surface, which is attached by ligament to the summit of the neural arch of the first dorsal vertebra. The first true neural plate, si, is much narrower, and is connate with the summit of the neural spine of the second dorsal vertebra ; the succeeding vertebral neural plates, S2 — ss, have the same relations with the succeeding neural spines, but the ninth, tenth, and eleventh, like the nuchal {ch) and pygal {j}i/), plates are independent ossifications in the substance of the derm. The costal pieces of the carapace are supra-additions to eight pairs of pleurapophyses or vertebral ribs, those, viz. of the second to the ninth dorsal vertebrae inclusive. The slender or normal portions of the ribs project freely for some distance beyond the expanded and connate portions (" costal plates" of the carapace), along the under surface of which the rib may be traced, of its ordinary breadth, to the neck and head, which liberates itself from the costal plate to articulate to the interspace of the two contiguous vertebral bodies, (centrums), to the posterior of which such rib properly belongs. The woodcut (fig. 2) illustrates this structure : ch shows the inner side of the nuchal plate ; c\ is the first rib, articulated to the fore part of the body of the first dorsal vertebrae ; ph is the first rib of the carapace (the second rib of the dorsal series), connate with the first costal plate ; ph to jih, are the succeeding ribs and costal plates of the carapace, the interspaces between their own vertebral body, and that of the preceding vertebra luucr view of carapace of the Loggerhead (Chelone caouanna). The heads of the ribs articulate to BRITISH FOSSIL REPTILES. Fig. 3. The tenth vertel)ra supports a short pair of ribs in Chelone and in Enn/s, but not in Trionyx; and this vertebra is commonly reckoned as a " kuiibar" one. The eleventh and twelfth vertebrae have short and thick ribs, which abut against the iliac bones, and they are regarded as forming the sacrum. The remaining vertebrae belong to the tail, and are " caudal." The costal plates articulate with each other, and with the neural plates by fine dentated sutures. The free extremities of the ribs are implanted into sockets of those marginal plates which are opposite to them. The 1st, 2d, 3d, and 10th, are not so articulated in the loggerhead turtle. But all the marginal plates articulate with each other, and with the nuchal [ch) and pygal {'py) plates by sutures. The osseous basis of the plastron consists of nine pieces, one single and sym- metrical, the rest in pairs. The median piece, *, is the entosternal ; the anterior pair, es, is the episternal ; the second pair, hs, the hi/osternal ; the third pair, ps, the Jiyposfernal ; and the posterior pair, xs, the xiphisternal. With regard to the nature or homologies of these bones, three views have been taken. The one generally adopted, on the authority of Cuvier, Bojanus, and GeoflFroy St. Hilaire, is, that the nine bones of the plastron are subdivisions of a vastly expanded sternum, or breast-bone ; the second view is, that these subdivisions of the sternum are enlarged by combination with ossifications of the in- tegument ;* and the third view, in which Rathke stands alone, is, that they are exclusively dermal bones, and have no homologues in the endoskeleton of other vertebrata.f Since this opinion is given as the result of that celebrated embryologist's observations on the de- velopment of the Chelonian reptiles, 1 have tested it by a series of similar researches on the embryos and young of the Chelone mydas and Testiah indica, and have been led by them to conclusions distinct from any of the three theories above cited. The sternum, like the carapace, is, without doubt, a compound of connate endo- skeletal and cxoskeletal pieces ; but the endoskeletal parts are not exclusively the homologues of the sternum. For the details of the observations, and the special arguments on which these conclusions arc founded, I must refer to the description of PI. 1, and to my paper in the 'Transactions of the Royal Society,' 1849; the homologies of the endoskeletal parts of the plastron will require a brief illustration here from comparative anatomy. * Peters, Observatioues ad Anatomiam Cheloniorum, 1838. t Ueber die Entwickelung der Schildkroten, 4to, 1848, p. 122. Bonos of the plastron of the Loggerhead Turtle (Cliclone caouamid). CIIELONIA. GeofFroy St. Hilaire, whose views are generally adopted, was guided in his deter- mination of the parts of the plastron by the analogy of the skeleton of the bird : which analogy may be illustrated by the subjoined dia- grams of corresponding segments of the thorax of a bird (fig. 4) and of a tortoise (fig. 5). In both figures c is the centrum or vertebral body ; ns the neural arch and spine ; compressed in the bird, depressed and laterally expanded, accord- ing to Geoffroy, in the tortoise ; pi the pleura- pophysis, or vertebral rib, expanded in the tortoise, and with its broad tubercle articu- lating with the expanded spine ; h, li. in fig. 5, answers to h in fig. 4, and is the lipemapo- physis (sternal rib, or ossified cartilage of the rib) ; h, lis in fig. 5, is ha in fig. 4, i. e. exclusively a sternum, with the entosternal piece, hs , developed hori- zontally in the tortoise, and vertically in the bird. 'Yh.Q prima facie simplicity of this view has imposed upon most comparative anatomists : and yet there are other vertebrate animals more nearly allied to the Chelonia than birds, and with which, therefore, comparison should have been insti- Fis. i. Thoracic sej^meut of tlie skeleton of a Bird. Fig. 5. tuted before general consent was yielded to the Geoffroyan hypothesis. If, e. g. we take the segment of a crocodile's skeleton (fig. 6) corresponding with that of the tortoise (fig. 5), the comparison will yield the following interpretation : in both figures c is the centrum : ns the neural arch and spine, with d the diapophysis ; sc a median dermal bony plate (connate with ns in the tortoise) ; pi the pleurapophysis ; sc sc lateral dermal bony plates (connate with pi in the tortoise) ; h, U in fig. 5, answers to li! in fig. 6, an intercalated, semi-ossified piece between pd and k in the crocodile ; h, hs in fig. 5, answers to h, the haemapophysis in the crocodile ; and hs in fig. 5, exclusively represents hs, the sternum in the crocodile. h s lit Thoracic segment of the skeleton of a Tortoise. Fiir. (■). Thoracic segment of the skeleton of a Crocodili 6 BRITISH FOSSIL REPTILES. Such a comparison, in my opinion, guides us to a truer view of the homologies of the thoracic-abdominal bony case of the Chelonians, especially with regard to the lateral or parial pieces of the plastron, than the comparison exclusively relied on by Geoffroy St. Hilaire. The Plesiosaurus, by its long and flexible neck, small head, expanded coracoid and pubis, and flattened bones of the paddles, comes much nearer to the turtle than the crocodile does ; and its abdominal ribs, or hfemapophyses, are more developed than in the crocodiles ; a comparison of the ventral surface of the skeleton, such as that figured by Dr. Buckland, in his ' Bridgewater Treatise,' vol. ii, pi. 18, fig. 3, will show how clearly those abdominal ribs would correspond with the hyosternals and hyposternals of the turtle, if they had coalesced together at their middle parts, leaving their outer and inner extremities free. With regard to the marginal pieces m\ — «?12, figs. 1 and 2, although the comparisons illustrated by figs. 4, 5, 6, show that they answer rather to the intercalated piece // in the crocodile than to the entire sternal rib h in the bird ; yet the phenomena of their development demonstrate that they are exclusively bones of the dermal skeleton, retaining their freedom from anchylosis with the endoskeletal elements, hke the nuchal, pygal, and last three neural plates {ch, py, sg, s\o, and .s-il, fig. 1). This insight into their true nature teaches why they do not correspond in number with the vertebral ribs or pleurapophyses (ph — p/s, fig- 2). In the loggerhead turtle, for example, the first three and the tenth (?/?i, ni2, m's, and m\o) have no corresponding pleur- apophyses articulating with them ; and if even ci be supposed to correspond to ms, there are no rudiments of ribs answering to mi and ?«2. The marginal plates are not constant in number ; the Clielone mi/das has two less than the Chelone caouanna has. Some species of Trionyx {Cryptopua, Dum. and Bibron) have a greater number, but of smaller and less regular size, confined to the posterior part of the limb of the carapace; in other species of Trionyx {Gymnojms, Dum. and Bibron), and in Spharyis, the marginal part of the carapace retains its embryonic condition in all Chelovia, as a stratum of cartilaginous cells in the substance of the derm, forming the thickened, flexible border of the carapace. The rudiments of the hyosternals and hyposternals (PI. 1, fig. 2a) have originally the form of sternal or abdominal ribs ; extend transversely, and rise at their outer extremities to join those of the first and sixth pair of vertebral ribs, completing the hsemal, or inferior vertebral arch (ib., fig. 14), without the interposition of any of the marginal pieces, which are merely applied to the outer sides of the haemapophysis or sternal ribs. The expansion of the parts of the plastron, especially in the fresh- water and land tortoises, is due chiefly to the ossification of a layer of cartilage-cells in the substance of the derm, which ossified plates are connate with the more internal elements of the plastron, representing the sternum and sternal ribs. In the following descriptions of the fossil Chelonia, the terms ' entosternal, episternal, hyosternal, hyposternal,' and ' xiphisternal,' will be used as absolute designations of the combined endoskeletal and exoskeletal bones of the plastron, wdthout implying assent to the hypothesis that first suggested those names to Geofi"roy St. Hilaire. CHELONIA. 7 The scapular and pelvic arches, and the bones of the extremities of the Chelonia, are described and figured in the ' Ossemens Fossiles' of Cuvier ;* where, also, the figures of the modifications of the carapace and plastron, in the fresh- water and land tortoises, will sufiice for the purpose of ulterior comparisons with the fossils described in the present work, if they be understood according to the homologies above discussed, and which are illustrated by the figures 1 and 2 of the carapace, and fig. 3 of the plastron of the Chelone caouanna. § 2. Family Marina. Genus Chelone. With regard to the more immediate subjects of the present chapter, it must be admitted that the important generalizations of Cuvier and Dr. Bucklandf have been confirmed, but not materially extended, by subsequent observations on the remains of reptiles of the Chelonian order. Cuvier, after admitting that his results in regard to the tortoises were not so precise as those relating to the crocodiles, sums up his chapter on the fossil Chelonia in the following words : "Toutefois nous avons pu nous assurer que les tortues sont aussi anciennes dans le monde que les crocodiles ; qu'elles les accompagnent gcneralement, et que le plus grand nombre de leurs debris appartenant a des sous-genres dont les especes sont propres aux eaux donees ou a la terre ferme, elles confirmentles conjectures que les os de crocodiles avoient fait naitre sur I'existence d'iles ou de continens nourissant des reptiles, avant qu'il y ait eu des quadrupcdes vivipares, ou du moins avant qu'ils aient ete assez nombreux pour laisser une quantite de debris comparable a ceux des reptiles.";}: - Dr. Buckland also states, in general but precise terms, that " the Chelonian reptiles came into existence nearly at the same time with the order of Saurians, and have continued coextensively with them through the secondary and tertiary formations unto the present time. Their fossil remains present also the same threefold divisions that exist among modern Chelonia into groups, respectively adapted to live on land, in fresh water, or the sea."§ The remains of sea turtles ( Chelone) have been recognised in the Muschelkalk, the Wealden, the lower cretaceous formation at Claris, and the upper chalk-beds at Maestricht. Figures of Chelonites, as that in the Frontispiece to Woodward's ' Synoptical Table of British Organic Remains,' and in Konig's ' Icones Sectiles' (pi. xviii, -fig. 232, a and b), have been published ; but no true marine Chelonian, from Eocene strata, had been scientifically determined prior to the communication of my Paper on that subject to the Geological Society of London. || All the Chelonites from * Tom. V, pt. 2, pi. xii and .xiii. t Bridgewater Treatise (183G), p. 2.5G. X Ossemeus Fossiles, 4to, torn, v, pt. ii, p. 2-J9. % Bridgewater Treatise, p. 256. II Proceedings of the Geological Society of London, vol. iii, pt. ii, p. 570, December 1, 1841. 8 BRITISH FOSSIL REPTILES. Sheppey, described and figured in the last edition of Cuvier's ' Ossemens Fossiles,' for example, are referred to the fresh-water genus Emys ; and the statement in tlie earlier edition of the ' Ossemens Fossiles,' that the greater part of the remains of Chelonian reptiles belong to the fresh-water or terrestrial genera, is repeated. The aim of the Memoir, communicated to the Geological Society in December, 1841, was to show that the conclusion deduced by Cuvier, from an imperfect carapace from Sheppey, which might probably have belonged to a species of Emys, had been unduly extended to other Chelonites, which undoubtedly belonged to the marine genus Chelone ; and that this genus was represented, in the Eocene strata, by at least six species ; the remains of five of which were from the London Clay at Sheppey, and those of a sixth were tolerably abundant in the cliffs near Harwich. In the carapace of the fossil Chelonian from Sheppey, communicated by Mr. Crowe, of Faversham, to Cuvier, and figured in the ' Ossemens Fossiles' (torn, v, part 2, pi. xv, fig. 12), the author of that great work conceived that all the characters of the genus Emys were perfectly recognisable. He points out the proportions of the neural plates, which are as long as they are large ; and in the figure they are represented of nearly a quadrate form, and not rhomboidal. The fifth neural plate in the fragment figured (probably the eighth) is separated from the sixth (ninth) by a point, which is made by the mesial ends of the fifth (probably the seventh) pair of costal plates ; a structure which Cuvier says slightly recalls what he had observed in the Jura Emys of Solcure.* But Cuvier admits that the neural plates {jihufirs vert eb rales) are narrower than those of existing Emydes ; and that the equal breadth of the ribs is a character common to the Cliehnes with the Emydes. Now, in reference to the carapace figured by Cuvier, it is to be observed, that the margins are wanting ; and that the broad conjoined portions of the costal plates are not longer than they might have been, had the fossil belonged to a turtle {Chelone) ; and, consequently, that there is no proof that they were united together by suture throughout their whole extent, as in the Emydes ; but that they might have terminated in narrow tooth-like processes, as in the Chehnes. The narrowness of the neural plates is a character which, with their smoothness, undoubtedly approximates the fossil to the Chehnes ; and, without intending to affirm that the fossil in question does not belong to the family ^wyt/iVfe, which unquestionably existed at the time of the deposition of the Sheppey clay, its determination appears to me to be much less decisive than mio-ht be inferred from the remarks in the ' Ossemens Fossiles.' * Tom. cit., p. 2.34. This structure is not, however, peculiar to the geiuis Emtjs ; in the carapace of the Chelone caouaniin, iu the Museum of the Royal College of Surgeons, the seventh neural plate is separated from the eighth by the junction of the expanded extremity of the seventh rib on one side -with that of the opposite rib, and the eighth neural plate from the ninth by the same modification of the eighth pair of rib ;. A similar modification may also be seen in the carapace of the Trionyx Henrici, PI. 6. CHELONIA. • 9 Mr. Parkinson describes the plastron of a Sheppey Chelonite,* in which the hyosternal and hyposternal pieces are not united, but leave a vacancy in the middle, which he conjectured may have been filled up by membrane. This specimen must have belonged to a specimen at least four inches in length, exclusive of the head and neck. But Cuvier supposes that it may, nevertheless, have belonged to an Emys ; and that the vacancy of the bony sternum merely indicated the nonage of the individual. t The grounds on which Cuvier refers to the genus Emt/s, the imperfect and dislocated carapace and plastron of M. Bourdet's Sheppey Chelonite,;}: are not detailed ; but it is evident that the hyposternals in that specimen are in contact at the posterior moiety of their median margins only ; and that the margins recede anteriorly, leaving a median interspace ; which, as the plastron is nearly a foot in length, can hardly be attributed to the immature state of the individual. And if, as Cuvier supposes, this specimen belongs to the same species as those in the collections of Messrs. Crowe and Parkinson, the same objection to their belonging to a fresh-water tortoise holds good, as to the one figured by M. Bourdet. The question of the reference of these Eocene fossils to the fresh- or sea-water families of the Chelonian order, seems to me to admit of the safest determination by examining the crania of the Sheppey Chelonites ; since the differences in the extent to which the temporal fossse are protected by bone, and in the proportions in which the bones enter into the formation of that covering, are strongly marked in the genera Emi/-s and Chelone. But here Cuvier appears to have been unusually biassed in favour of the Emydian nature of the Sheppey fossils ; for in reference to the cranium, figured by Mr. Parkinson, the affinities of which to the turtle's skull will be presently pointed out, Cuvier obsei'vcs : " elle est probablement aussi d'une Emyde, bien qu'elle participe des caracteres de Tortues de Mer, par la manicre dont le parietal recouvre sa tempe ; mais nous avons vu que VEmys exjjansa differe tres peu de Tortues de Mer a cet egard, et la partie anterieure de la tete fossile ressemble d'avantage a celle d'une Emyde qu' a celle d'une Chelonce, surtout par le peu de largeur de I'intervalle des yeux."^ Now the most striking difference between the temporal bony vault of the Emys expansa and that of any known species of Chelone, is seen in the diminutive size of the post-frontals in this exceptional case among the Emydes, as contrasted with their large size and actual extension over the temporal fossse in the Chelones : — and this difference is accompanied by a proportional diminution in the breadth of the parietals in the true marine turtles. * Organic Remains, vol. iii, p. 268, pi. xviii, fig. 2. f Ossemens Fossiles, torn, v, pt. ii, p. 23.5. X Tom. cit., pi. XV, figs. 14-15. § Tom. cit., p. 235. C 10 BRITISH FOSSIL REPTILES. But the figure in Parkinson's work gives clearly the latter character ; whence also we may infer that it agreed more with the Cheloncs also in the size of the postfrontals ; although the anatomy of the skull is too obscurely delineated to demonstrate this fact. The following important affinities are, however, unquestionably indicated in Parkinson's figure :— first, the large size of the orbits, which are nearly six times greater than those of the Emi/s expanm ; secondly, their more posterior and lateral position ; and Ikirdh/, the greater breadth of the interorbital space : in all which characters the Sheppey fossil closely resembles the true Chelojies, and differs from the only known species of Emys {Podocnemi/s) expansa, in which the temporal openings are protected by a bony roof. That fresh-water tortoises have left their bony cuirasses in the Sheppey clay, will be subsequently shown ; but the evidence of the genus Emi/s, adduced by Cuvier, is incompetent to prove their existence ; and, it may be affirmed, that of the fossils cited by the founder of Palaeontology, some, with great probability, and others with certainty, are referable to the marine genus, Chelone. Without further discussing the question as regards these evidences, I shall proceed to describe the specimens from Sheppey which I have myself had the opportunity of examining ; and shall commence with those which belong undoubtedly to the marine family. Chelone breviceps. Oicen. Plates 16, 17, \1 A. Proceedings of the Geological Society, December 1, 1841; Report on British Fossil ReptUes, Traus. British Association, 1841, p. 1/8. Syn. Emys Parkixsonii. J. E. Gray. — DE Sheppey. FI. v. Meyer (I). Chelone antiqua. Kcenig (?). The first of the Chelonites, which led me to the recognition of this species, was a nearly perfect cranium from Sheppey (PI. \7A, figs. 1 — 4), wanting only the occipital spine, and presenting a strong and uninterrupted roof, extended posteriorly from the parietal spine on each side (figs. 1 and 4, 7), over the temporal openings to the mastoids (ib. 8) ; and formed anteriorly by a great development of the posterior frontals (figs. 1 and 2, 12). This unequivocal testimony of the marine genus of the fossil, is accompanied by similar evidence afforded by the large size and lateral aspect of the orbits (fig. 1, or), the posterior boundary of which extends beyond the anterior margin of the parietals ; and by the absence of the deep emargination which separates the superior maxillary (ib, 21) and malar (20) from the squamosal (27) and the tympanic bone (28) in the fresh- water tortoises, and especially in the Fodocnemys expansa. In general form, the skull of the present species of Sheppey turtle resembles that of the Chelone mi/das, Brongn. : but it is relatively broader ; the prefrontals (figs 1 and CHELONIA. 11 2, 14) are less sloping, and the anterior part of the head is more vertically truncate. The orbits are relatively larger, and extend nearer to the tympanic cavity. The frontals (ib. 11) enter into the formation of the orbits in rather a larger proportion than in Chelone mijdas. In the Chelone caouanna* they are wholly excluded from the orbits. The trefoil shape of the occipital tubercle is well marked (fig. 4) ; the depression in the basioccipital, bounded by the angular pterygoid ridges, is as deep as in most true turtles (fig. 3, 1) ; the lateral borders of the expanded parietals are united by a straight suture along a great proportion of their extent to the large postfrontals. These proportions are reversed in the Podocnemys expanm, in which the similarly expanded plate of the parietals is chiefly united laterally with the squamosal and tympanic bones. In other fresh-water tortoises the parietal plate in question docs not exist. The same evidence of the affinity of the Sheppey Chelonite in question to the marine turtles, is afforded by the base of the skull (fig. 3) ; the basioccipital (1) is deeply excavated ; the processes of the pterygoids (24), which extend to the tympanic pedicles, are hollowed out lengthwise : the palatal processes of the maxillary and palatine bones are continued backwards to the extent which characterises the existing OliL'hnes ; and the posterior or internal opening of the nasal passages, is, in a pro- portional degree, carried further back in the mouth. The lower opening of the zygomatic spaces is wider in the present Sheppey Chelonite, than in Podocnemys ew2Xt)isa. The external surface of the cranial bones in the fossil is roughened by small irregular ridges, depressions, and vascular foramina, which give it a wrinkled or shagreen-like character. The following are dimensions of the specimen described : Licbes. Lines. Length of cranium from the occipital condyle ... 2 9 Breadth of cranium across the malars (26) .... 2 7 Antero-po.sterior diameter of orbit ..... 1 The lower jaw, which is preserved in the present fossil, likewise exhibits two characters of the marine turtles ; the dentary piece (fig. 3, 32), e. y. forms a larger pro- portion of the lower jaw than in the land or fresh-water tortoises. The joint of the rami is completely obliterated at the symphysis, which is not longer or larger than in Chelone viydas. The species represented by this fossil, which is preserv^ed in the British Museum, and by a very similar one in the Hunterian Collection (PI. 1 7, figs. 1 — 5), is selected for the first of the Eocene Chelonians to be described in the present Work, because it is one of the few with which the characters of the carapace and plastron can with certainty be associated with those of the cranium. In the rich collection of Sheppey fossils, belonging to J. S. Bowerbank, Esq. F.R.S. * Ossem. Fossiles, torn, v, pt. ii, pi. xi, fig. 2. 12 BRITISH FOSSIL REPTILES. there is a l)eautiful Chelonite (PL 16, figs. 1, 2) including the carapace, plastron, and the cranium, which is bent do\\Ti upon the fore part of the plastron ; and which, though mutilated, dis2)lays sufficient characters to establish its specific identity with the skull of the Chelone brevicej^s just described. Both the carapace and plastron present the same finely rugous surface externally as the cranium ; in which character we may perceive a slight indication of affinity with the genus Trionyx, The carapace (PI. 16, fig. 1) is long, narrow, ovate, widest at its anterior half, and tapering towards a point posteriorly ; it is not regularly convex, but slopes away, like the roof of a house, from the median line, resembling, in this respect, and its general depression, the carapace of the turtle Chelone mydas. There are preserved the nuchal plate (fig. 1, e/<*) with ten of the neural plates {u\ — ?^lo*), only the eleventh and pygal plates being wanting. The eight pairs of costal plates {pl\ — -ph) are also present, with sufficient of the narrower tooth-like extremities of the six anterior pairs of ribs, to determine the marine character of the fossil, which is indicated by its general form.f The nuchal plate (fig. 6, ch) is of a transversely oblong form, with the anterior margin gently concave. Its antero-posterior diameter, or length, is ten lines ; its transverse diameter, or breadth, is two inches. The lateral margins are bounded by two lines meeting at a slight angle ; to the anterior one, the first of the marginal plates, «n, is attached; the posterior line bounds part of the vacant interspace between the first costal plate (jy/l), and the anterior marginal plate. The presence of this plate would prove for the genus Chelone as against Trionyx, were the characters of the cranium, the impressions of the vertebral scutes, and the sternum wanting. The nuclial plate in the Emydes is hexagonal, and nearly as long as it is broad. The Chelonite from the tertiary beds near Brussels, figured by Cuvier,:}: has the nuchal plate of nearly the same form as the present specimen from Sheppey. The neural plates in the Chelone breviceps axQ as narrow as in the Chclones generaWy ; and as in the Brussels Chelonite above cited. The first neural plate (.si, fig. 1) is four-sided; the rest, to the eighth («8), are hexagons of a more regular figure than in the existing Chelones, and are articulated to more equal shares of the contiguous alternate costal plates {ph — ph).* The first costal plate {ph) is directed more outwards, does not incline backwards, as in recent Chelones, and its anterior angle is less truncated than in them. (See fig. 1, p. 3.) The length of the second costal plate [ph) is one inch, nine lines ; more than half of the narrow terminal extremity of the connate rib is preserved ; the propoitions of * These letters refer to the parts in the typical carapace fig. 1, p. 3, by reference to which the cor- icspondiiig parts in the fossil will be readily under.stood. f In an Emijs with a carapace seven inches in length, the corresponding extremities of the ribs would have been united together by the laterally-extended ossification. X Osi-emens Fossiles, torn, v, pt. 2, pi. xv, fig. IG. CHELONIA. 13 the remaining costal plates correspond with those of the Chelone mydas, and Cliel. caouanna. The last pair of costal plates [ph) articulates with the eighth, ninth, and tenth neural plates, but does not overlap or supersede any of them. Not any of the costal plates articulate with those of the opposite side, so as to inteiTupt the series of vertebral plates, as in the carapace of the Chelone caouanna (fig. 1, p. 3), as in Mr. Crowe's Sheppey Chelonite, figured by Cuvier (torn. cit. pi. xv, fig. 12) ; and as is shov^ai in the view of the concave surface of the Brussels species (torn. cit. pi. XV, fig. 16). The ninth neural plate (fig. 1, sg) is the narrowest, as in the Chelones, and as in the Brussels Chelonite, figured by Cuvier, in loc. cit. pi. xiii, fig. 8, instead of beino- suddenly expanded, as in most Emydes. The tenth neural plate («io) expands to a breadth equal with its length ; the eleventh and pygal plates, as already observed, are wanting in the fossil. The vertebral or median ends of the costal plates present a modification of form, corresponding with that of the interspaces of the neural plates to which they are articulated. Only the first pair {pl\) present that form which characterises all but the last pair in the existing Chelones, and in the Brussels Chelonite ; viz., a straight line with the posterior angle cut off; the rest being terminated by two nearly equal oblique lines, meeting at an open angle, as shown in PI. 16, fig. \,pl'l — ph. This character would serve to distinguish the Chelone breviceps, if only a portion of the carapace, including the vertebi-al extremity of a rib, were preserved. The free extremities of the ribs are thicker in proportion to the costal plates, than in the Chelone caouanna, or the Chel. mydas ; and more resemble, in this respect, those of the Chel. imbricata, the species characterised by the size and beauty of the horny scutes, commonly called " tortoise-shell." More or less complete impressions of the five horny vertebral scutes {v\ — vb), and of four costal scutes on each side of the vertebral ones, show the forms and proportions of these characteristic parts, and especially of the median series, notwithstanding they were among the soluble and perishable elements of this ancient turtle of the Thames. The hexagonal vertebral scutes are characterised by the near equality of their sides, and the angle of about 100°, at which the two outer sides meet. The anterior border of the first vertebral scute, i^, has crossed and impressed the nuchal plate, ch, near its anterior border ; this scute has covered the rest of the nuchal plate, and more than half of the first neural plate. The second vertebral scute, v-, includes the rest of the first neural plate, the whole of the second, and almost the whole of the third neural plate. The third vertebral scute, ^;^ includes the hind border of the third neural plate, with the whole of the fourth and fifth neural plates. The fourth vertebral scute includes the sixth and seventh, and very nearly the whole of the eighth neural plates, and the outer angles of this scute terminate over the suture between the sixth and seventh costal plates. 14 BRITISH FOSSIL REPTILES. The plastron of the Chelone brcviceps (PI. 16, fig. 2), although more ossified than in existing Chelones, yet presents all the essential characters of that genus. There is a central vacuity left between the hyosternals {lis)* and hyposternals {ps); but these bones differ from those of , the young Emi/s in the long pointed processes which radiate from the two anterior angles of the hyosternals {hs), and the two posterior angles of the hyposternals {ps)* The xiphisternals [xs) have the slender elongated form, and oblique union by reciprocal gomphosis with the hyposternals {hs), which is characteristic of the genus Chelone. The posterior extremity of the right episternal {es) presents the equally characteristic, slender pointed form. With these proofs of the modification of the plastron of the present fossil according to the peculiar type of the marine Chelones, there is evidence, however, that it differs from the known existing species in the more extensive ossification of the component pieces ; thus the pointed rays of bone extend from a greater proportion of the margins of the hyosternals and hyposternals ; and the intervening margins do not present the straight line at right angles to the radiated processes. In the Chelone mi/das, and Chel. caouanna (fig. 3, p. 4), for example, one half of the external margin of the hyosternal and hyposternal, where they are contiguous, are straight, and intervene between the radiated processes, which are developed from the remaining halves, while in the Chelone hreviceps, about a sixth part only of the corresponding external margins are similarly free, and there form the bottom, not of an angular, but a semicircular interspace. The radiated processes from the inner margins of the hyosternals and hyposternals, are characterised in the Chelone breviceps by similar modifications, but their origin is rather less extensive ; they terminate in eight or nine ra3^s, shorter, and with intervening angles more equal than in existing Chelones. The xiphisternal piece, xs, receives in a notch the outermost ray or spine of the inner radiated process of the hyposternal, as in the Chelones, and is not joined by a transverse suture, as in the Emydes, whether young or old. Subjoined are dimensions of the plastron of Mr. Bowerbank's fossil : Inches. Lines. Shortest longitudinal diameter of hyosternal and hyposternal pieces 2 .5 Transverse diameter of ditto ...... 1 7 Total length of plastron ....... 6 The bones of the scapular arch, especially the coracoid, Cuvier has shown to afford distinctive cliaracters of the natural families of the Chelonia ; but the Eocene Chelonites described Jjy Cuvier, did not yield him this opportunity of thus testing their affinities. In the Chelone breviceps here described, the left coracoid (shown in fig. 2) is jireserved in nearly its natural position ; it is long, slender, symmetrical ; cylindrical near its humeral * These letters refer to the parts in the typical plastron, fig. 3, p. 4, by reference to which tlic homo- logous parts in the fossil will be readily understood. CHELONIA. 15 extremity ; flattened, and gradually expanded from its humeral third, to its sternal end; which is relatively somewhat broader than in the Chelonc mi/das and Chdonc caouanna. Inch. Lines. Its length is ..... 1 6 Breadth of sternal end ... 7 The characters thus afforded by the cranium, carapace, plastron, and by one of the bones of the anterior extremity, prove the present Sheppey fossil to belong to a true sea turtle ; and at the same time most clearly establish its distinction from the known existing species of Ch(?lone. On account of the shortness of the skull, especially of the facial part and of that which intervenes between the orbit and ear, compared with the breadth of the skull across the mastoids, I have proposed to name this extinct species, Chelone breviceps* By the characteristic shape of the median extremities of the costal plates of the carapace, I have been able to determine some fragmentary Chelonites which have afforded better ideas of the size of the species represented by Mr. Bowerbank's more complete but immature specimen of Chelone brevicejjs. A portion of the carapace of the Chelo-ne breviceps, including the fourth, fifth, sixtli, and part of the third and seventh neural plates, with a considerable proportion of the third, fourth, fifth, and sixth costal plates, is preserved in the museum of Mr. Robertson, of Chatham. The characters of the rugous surface of these bones, and of the equal- sided angles by which the costal plates articulate with the neural plates, do both, and especially the latter, point out the species to which the present fragment belongs. It has formed part of an individual double the size of the specimen above described, and figured from Mr. Bowerbank's collection, and therefore it had a carapace sixteen inches in length. Although the costal plates have been continued further along the ribs than in the younger example, the more complete state of the sixth rib, in Mr. Robertson's specimen, shows that they retained their longitudinally-striated, tooth-like extremities, which, in the sixth rib, is two thirds of an inch in length ; the length of the expanded part being four inches, and its breadth one inch nine lines. The internally prominent part of the rib is much less developed than in Chelone planimentim , and Chelone crassicostata, afterwards to be described. The right hyostcrnals and hyposternals are present, and they likewise preserve the character of the Chel. breviceps in their rugous surface and minor breadth, as compared with those parts in the Chelone lon(jiccps, the extinct species next to be described. Besides the specimens above described, on which the present extinct species of turtle * Proceedings of Geological Society, December 1, IS II, p. 570. Report on British Fossil Reptiles, Trans. Brit. Association, 1841, p. 178. 16 BRITISH FOSSIL REPTILES. has been established, remams of the Chelone hreviccps are preserved in the Hunteriau Museum, and in that of my esteemed friend Professor Bell, S.R.S. I know no other locality of the species than that of Sheppey, in Kent. Chelone longiceps. Owen. PI. 12 and 13. Proceedings of Geological Society of London, December 1, 1841, p. 572. Report on British Fosiil ReptUia, Trans. British Association, 1841, p. 177. The second species of Chelone, from the Eocene clay at Sheppey, which I originally recognised and defined by the fossil skull (PI. 1 2) differs more from those of existing Chelones by the regular tapering of that part into a prolonged pointed muzzle, than does the Chelone brevicejjs by its short and anteriorly-truncated cranium. The surface of the cranial bones is smoother than in the Chel. brcviceps ; whilst their proportions and relations prove the marine character of the present fossil as strongly as in that species. The orbits (PI. 12, figs. 1 and 2, o,) are large ; the temporal fossae (ib. fig. 3) are covered principally by the posterior frontals (fig. 2, 12), and the osseous shield completed by the parietals (7), and mastoids (s), overhangs the tympanic (28), ex- occipital (2), and paroccipital (4) bones. The compressed spine (3)* of the occiput is the only part that projects further backwards. The palatal and nasal regions of the skull afford further evidence of the affinities of the present Sheppey Chelonite to the true turtles. The bony palate (fig. 3) presents, in an exaggerated degree, the great extent from the intermaxillary bones to the posterior nasal aperture which characterises the genus Chelone ; and it is not perforated, as in the soft turtles {Trioni/x), by an anterior palatal foramen. The extent of the bony palate is relatively greater than in the Chelone mt/clas, and the trenchant alveolar ridge is less deep ; the groove for the reception of that of the lower jaw is shallower than in the Chelone mydas, or the extinct Chel. breviceps, arising from the absence of the internal alveolar ridge, in which respect the Chel. longiceps resembles the Chel. caretta. The Chelone lonjjiceps is distinguished from all known existing Chelones by the proximity of the palatal vomer (13, fig. 3), to the basisphenoid (5), and by the depth of the groove of the pterygoid bones (24),* and in both these characters in a still greater degree from the Trionyxes ; to which, however, it approaches in the elongated and pointed form of the muzzle, and the trenchant character of the alveolar margin of the jaws. The followinsr are dimensions of the skull described: Inches. Liues, 4 2 6 1 2 Length of the skull ....... Breadth of ditto across the zygomata .... Antero-posterior diameter of orbit ..... * The smaller figures are placed on the parts in Pis. 11 and 17^, by comparison with which the tor- responding bones of the present skull will be readily discerned. CHELONIA. 17 • In a second example of the skull of Chelone longiceps, two of the middle neural plates, and the corresponding costal plates of the right side, portions of vertebrae, with the right xiphisternal piece, humerus and femur, are cemented together, and to the cranium by the petrified clay. The neural plates in this specimen are flat and smooth ; the entire one measures one inch two lines in length, and nine lines across its broad anterior part :— this receives the convex posterior extremity of the preceding plate in a corresponding notch. A small proportion, about one sixth, of the anterior part of the external margin, joins the second costal plate ; the remaining five sixths of the outer margin forms the suture for the vertebral end of the third costal plate. In this respect, the Chel. longicqjs resembles the existing Chelones ; and differs, as well as in the smooth and flattened surface of the vertebral plates, from the Chelone breviceps. The length of the third costal plate, in the fragmentary example here described, is three inches ; the impression of the commencement of the narrow portion, formed by the extremity of the coalesced rib, is preserved. The marginal indentations of the vertebral scutes are not half a line in breadth. The transverse impression between the first and second vertebral scute crosses the first neural plate, nine lines from its posterior extremity ; the second neural plate is free, as in other Chelones, from any impression, being wholly covered by the second vertebral scute. The expanded ribs are convex at the under part, slightly concave at the upper part in the direction of the axis of the shell ; they slope very gently from the plane of the neural plates, about half an inch, for example, in an extent of three inches ; thus indicating a very depressed form of carapace. The xiphisternal bone, like that of Cltel. breviceps, is relatively broader than in the existing turtles, and both the internal and external margins of its posterior half are slightly toothed. A part of the notch by which it was attached to the hyposternal remains upon the broken anterior extremity of the bone. It measures one inch two lines across its broadest part ; its length seems to have been three inches and a half. The humerus presents the usual characters of that of the Chelones ; its length is two inches three lines ; its breadth across the large tuberosities ten lines. The radius and ulna extend in this Chelonite from beneath the carapace into the right orbit ; the radius is one inch and a half in length ; the ulna one inch, three lines in length ; portions of vertebrae adhere also to the mass, the state of which indicates that the animal had been buried in the clay before the parts of the skeleton had been wholly disarticulated by putrefaction. A mass of Sheppcy clay-stone supporting the ninth and tenth neural plates, and the expanded portions of the sixth, seventh, and eighth costal plates of the right side, exhibits the characters of the marine turtles in the great relative expansion of the D 18 BllITISH FOSSIL REPTILES. tenth neural plate ; and the tooth-like continuation of the rib from the posterior angle of the eighth costal plate. These portions of the carapace, from their smooth surface, the impressions of the homy scutes, the form of the vertebral ends, and the concavity of the upper surface of the costal plates, evidently belong to the same species as the fossil last described. A similar mass of Sheppey clay-stone, in Mr. Lowe's collection, supports a larger proportion of the hinder part of the carapace, including the sixth, seventh, eighth, ninth, and tenth neural plates, part of the fifth neural plate, more or less of the last four pairs of costal plates, with the impressions of the third and fourth ribs of the right side ; the impression of apparently the whole of the free, slender, termination of the third rib is preserved, and also that of the fifth rib, confirming the generic characters indicated by the skull. The smooth outer surface of the bones of the carapace, the forms of the neural plates, and the concomitant modification of the commencement of the costal plates articulated therewith, concur to establish the specific distinction from the Cliclone hreviceps, and indicate the specimen to belong to the present species, Cliehnc longiceps. The seventh, eighth, and ninth neural plates progressively decrease in size ; and the ninth presents a simple, quadrangular, oblong- form ; the tenth neural plate suddenly expands, and has apparently a triangular form, but its posterior border is incomplete. The indications of the comparative flatness of the carapace of the Chelone longiceps, (in this respect, as in the elongated and pointed form of the skull, approaching the genus Trio7ti/x,) which were derived from an examination of the foregoing fragments, and particularly of the portion preserved with the cranium on which the species is founded, are fully confirmed by the almost entire carapace and plastron (PI. 13) which, subsequently to the publication of my ' Report on British Fossil Reptiles,' where the present species is first noticed, I have had the opportunity of examining in the collection of Mr. Bowerbank. This carapace, as compared with that of the Chelone hreviceps in the same collection, presents the following differences : — it is much broader and flatter. The neural plates are relatively broader ; the lateral angle from which the intercostal suture is continued, is much nearer the anterior margin of the plate — the Cliclone longiceps, in this respect, resembling the existing species of turtle (see fig. 1, p. 3). The costal plates are relatively longer ; they are slightly concave transversely to their axis on their upper surface, while in Chel. hreviceps they are flat. The external surface of the whole carapace is smoother ; and although it is as depressed as in most turtles, it is more regularly convex ; not sloping away by two nearl)^ plane surfaces from the median longitudinal ridge of the carapace. The following minor differences may be noticed in the two Sheppey Chelonites : the nuchal plate of the Chel. longiceps (PI. 13, fig. 1, i) is more convex at its middle part, and sends backwards a short emarginate process to join the first neural CHELONIA. 19 plate (2) ; in which it resembles the Cliel. wi/Jas. The second neural plate (3) is pentangular, the left anterior corner being produced, and truncate to join with the first costal plate of the left side ; the right posterior corner of the first neural plate (2) being produced, and truncate, to articulate with the second costal plate of the right side. This structure I believe, however, to be an individual variety. In another carapace of the Chelone lon(jiceps, e. g. both posterior angles of the first neural plate are produced, and truncate to articulate with the second pair of costal plates ; and the second neural plate is quadrangular. But the characters of the species are exemplified in more constant modifications of the carapace. The succeeding neural plates to the seventh inclusive (4 — 7) are hexagonal, with the anterior lateral border much shorter than the posterior lateral border, as in Chelone mi/das, and not of equal extent, as in Chelone hreviceps ; they become more equal in the seventh (y) and eighth (9) neural plates, which also decrease in size ; the ninth plate (10) is very small, quadrangular, and oblong, as in Mr. Lowe's fragment. Only a small portion of the last neural plate is preserved in Mr. Bowerbank's beautiful specimen. The impressions of the horny scutes are deeper, and the lines which bound the sides of the vertebral scutes {vy — v-\) meet at a much more open angle than in the Chel. breviceps, in which the vertebral scutes have the more regular hexagonal form of those of the Chel. mi/das. Their relations to the neural plates are nearly the same as in Chel. breviceps. The plastron (PI. 13, fig. 2) is more remarkable than that of the Chel. brevicem for the extent of its ossification ; the central cartilaginous space being reduced to an elliptical or subquadrangular fissure. The four large middle pieces hyosternah {hs) and Injposternah (ps), have their transverse extent relatively much greater as compared with their antevo-posterior extent, than in the Chel. breviceps; and this might be expected, in conformity with the broad character of the bony cuirass indicated by the carapace. The median margins of the hyosternals (lis) are developed in short toothed processes, along their anterior three fourths ; the median margins of tlie hypiosternuls (ps) have the same structure along nearly their whole extent ; the intermediate space between the smooth or edentate margins of the opposite bone is ten lines ; the expanded end of the long coracoid is seen projecting into this space. The xiphisternals (xs) are relatively broader than in Chel. breviceps, or in any of the existing turtles ; and are united together, or touch each other, by the toothed processes developed from the whole of their median margins. The entosternal piece is broad, flat on its under surface, and is likewise dentated at its sides. The outer surface of each half of the jilastron inclines, as in the Chelone mydas, towards a submedian longitudinal ridge. The breadth of the plastron, in the specimen figured (fig. 2), along the median suture, uniting the hyosternals and hyposternals, is six inches : the narrowest antero- posterior diameter of the conjoined hyosternals and hyposternals is two inches nine lines 20 BRITISH FOSSIL REPTILES. The breadth of the plastron, at the junction of the xiphisternals with the hyposternals, is two inches six Hnes. The posterior part of the cranium is preserved in Mr. Bowerbank's specimen (fig. 1), withdrawn beneath the anterior part of the carapace ; the fracture shows the osseous shield covering the temporal fosste ; and the pterygoids remain, exhibiting the deep groove that runs along their under part. It is most satisfactory to have found that the two distinct species of the genus Chelone, determined, in the first instance, by the skulls only, should thus have been confirmed by the subsequent comparison of their bony cuirasses ; and that the specific differences, manifested by the cuirasses, should be proved by good evidence to be characteristic of the two species founded on the skulls. Thus the portion of the skull preserved with the carapace first described (PI. 17, fig. 6), served to identify that fossil with the more perfect skull of the Chelone breviceps (PI. 17, yl), by which the species was first indicated. And, again, the portion of the carapace adhering to the perfect skull of the Chelone longiceps equally served to connect with it the nearly complete osseous buckler (PI. 13, fig. 1), which, otherwise, from the very small fragment of the skull remaining attached to it, could only have been assigned conjecturally to the Chel. longiceps ; an approximation which would have been the more hazardous, since the Chelone breviceps and Chelone longiceps are not the only turtles which swam those ancient seas that received the enormous argillaceous deposits of which the Isle of Sheppey forms a part. Chelone latiscutata. Owen. Plate 24. Proceedings of the Geological Society of London, December 1, 1841, p. 574. Report on British Fossil Reptiles, Trans. British Association, 1841, p. 1/9. A considerable portion, measuring three inches in length, of the bony cuirass of a young turtle from Sheppey, including the first to the sixth neural plates (PI. 24, fig. 1, il — a'G), with the corresponding pairs of costal plates i^ph — ^^/g), and the hyosternal (fig. 2, hs) and hyposternal {ps) elements of the plastron, most resembles that of the Chelone longiceps in the form of the carapace, and especially in the great transverse extent of the above-named parts of the plastron : it diff"ers, however, from the Chel. longiceps, and the other known fossil Chelonites, in the greater relative breadth of the vertebral scutes {v% ws), whicii are nearly twice as broad as they are long. The central vacuity of the plastron is subcircular ; and, as might be expected, from the apparent nonage of the specimen, is wider than in the Chel. longiceps ; but the toothed processes given off from the inner margin of both hyosternals and hyposternals are small, sub-equal, regular in their direction, and thus resemble those of the Chel. longiceps ; the slender point of the episternal is) is preserved in the interspace between CHELONIA. 21 the hyosternals. Both hyostemals {//s) and hyposternals (ps) are slightly bent upon a median longitudinal prominence of their under surfaces. The length of the third costal plate (jjIs) is one inch seven lines ; its antero- posterior diameter or breadth, six lines : in the form of the vertebral extremities of the costal plates, and of the neural plates to which they are articulated, the present fossil resembles the C/iel. longiceps ; but the fifth neural plate is more convex, and is crossed by the impression dividing the third vertebral scute (I's) from the fourth, which impression crosses the suture between the fifth and sixth neural plates in both Chelone longiceps and Chelone breviceps. Whether, in the progressive change of form, which the vertebral scutes may have undergone in the growth of this young turtle, as during the growth of the young loggerhead turtle {Chelone caouanna), hy an increase of length, without corresponding increase of breadth, the impression between the third and forth vertebral scute, might also retrograde to the interval between the fifth and sixth neural plates, I am uncertain, having only had the opportunity of comparing the scutes of the young and old loggerhead turtles, not the skeletons. The change in the lateral angles of the vertebral scutes, resulting from the elongation of the scutes themselves, in the loggerhead turtle, would be similar to that in the Chelone loiifficejjs, as compared with the Chel. lafiscutafa, on the hypothesis that the latter is the young of the former ; but in my present uncertainty I prefer to indicate the specimen in question, by the definite name proposed in my original Memoir ; its description as a distinct species being more likely to attract the attention of Collectors to similar specimens, and to enable them to identify such. Figure 3 gives the degree of convexity of the carapace, and the double curve of the plastron produced by the prominence of the principal hsemapophyses hs ?iXi(\. ps. The left scapular arch (51) is exposed in this view. Chelone convexa. Oioen. Plate 14 and Plate 24, fig. 4. Proceedings of the Geological Society of Loudon, December 1, 1841, p. .575. Report on British Fossil Reptiles, Trans. British Association, 1841, p. 178. The fourth species of Chelone, indicated by a nearly complete cuirass, from Sheppey, holds a somewhat intermediate position between the Chelone breviceps and the Chelone longicejis ; the carapace being narrower, and more convex than that of Chel. longiceps ; broader and with a more regular transverse curvature than in the Chelone bre'oiceps. Although the specimen is equal in size to either of the two with which it is here compared, the costal plates hold an intermediate length, which shows that this character is not due to a difference depending upon age. The fossil in question includes the first to the eighth neural plate inclusive ; the first plate (2) expands behind, and both posterior angles are truncated to articulate with the second costal plates {pli). The second neural plate (3) is quadrate, half as long again as broad, and the second pair of costal plates articulate with this, as well 22 BRITISH FOSSIL REPTILES. as with the first and third plates, as in the specimen of Chel. lonpceps noticed at p. 1 9. The tooth-like extremity of the connate rib is preserved on the right side. The fomth costal plate {ph) is two inches four lines in length, nine lines in breadth ; the angle at which the expanded part contracts to the extremity of the connate rib is well shown on the right side. The third to the eighth neural plates expand anteriorly, and have the anterior angles cut off to articulate with the costal plates in advance ; they diminish in size very gradually, and the antero-lateral borders, formed by the above-named truncated angles, do not increase in length as in the corresponding plates in the Chelone lonyiceps. The vertebral scutes (u2, vz, va) resemble more in form those of the Chel. lonyiceps than of CJicl. hreviceps ; but, notwithstanding that the whole carapace is narrower than in Chel. lonyiceps, the vertebral scutes are broader ; and the lines which converge to the lateral angle have a more marked sigmoid curvature. Chel. convexa. Chel. longiceps. Inclies. Lines Inches. Lines. The length of the second vertebral scute is 1 8 1 8 Breadth 2 (J 2 2 The two succeeding scutes (i'3 and va) more rapidly diminish in size than in either the Chel. breviceps or lonyiceps, and the transverse impression between the third and fourth vertebral scute crosses the lower third of the fifth neural plate, as in Chelone latiscutata. All the scutes have left deeper and rather wider impressions than in the preceding species. The second to the fifth costal plates inclusive, are more equal in length than in the existing Chelone mjdas or Chel. caouanna, and in this character the present species more resembles the Cliel. hnhricata. The distinction of the present from the previously described fossils, already manifested in the structure of the carapace and the form of the vertebral scutes, is more strikingly established in that of the plastron (PI. 14, fig. 2), which, in its defective ossification, resembles the same part in the existing species of Chelone. All the bones, but especially the xiphisternals [xs), are more convex on their outer surface than in other turtles, recent or fossil. The central vacuity is greater than in any of the above-described fossil species. The internal rays of the hyosternals come off from the anterior half of their inner border, and are divided into two groups : the lower consisting of two short and strong teeth, projecting inwards towards the extremity of the entostei:aial {s) ; while the rest extend forwards along the inner side of cpisternals [e.^). The same character may be observed in the corresponding processes of the hj/posternals {ps), which are limited to the posterior half of their inner border. The external radiated process of the hyosternals (/<*) arises from a larger proportion of the outer margin, than in tlie Chel. mydas ; but from a somewhat less proportion than in Cliel. breviceps. CHELONIA. 23 The external process of the hyposternal {ps) is relatively much narrower than in the Chel. hreviceps (PI. 16, fig. 2), and, a fortiori, than in C'/«?/. lonfficeps (PI .13, fig. 2). The straight transverse suture by which the hyosternals and hyposternals of the same side are joined together, is much shorter than in the other fossil Chelones ; and is similar in extent to that in CM. mi/das ; but the following differences present themselves in the plastron of the Chelone convexa, as compared with that of the Chelone mi/das. The median margin of the hyosternals forms a gentle curve, not an angle : that of the hyposternals is likewise curved, but with a sliglit notch. The longitudinal ridge on the external surface is nearer the median margin of the hi/osteriiah and huposternah and is less marked than in the Chelone longiceps ; especially in the hyposternals, which are characterised by a smooth concavity in the middle of their outer surface. Tlie suture between the liyosternals and hi/posterHals is nearer to the external, transverse, radiated process of the hyposternals. The median vacuity of the sternal apparatus is elliptical in the Chel. convexa, but square in the Chel. mydas. The characteristic lanceolate form of the episternal bone («) in the genus Chelone, is well seen in the present fossil. The cntosternal element of the plastron is sub- circular, or lozenge-shaped ; and generally broader than it is long in the Emydians. The true marine character of the present Sheppey Chelonite, so well given in the carapace and plastron, is likewise satisfactorily shown in the small relative size of the entire femur (65) which is preserved on the left side, attached by the matrix to the left xiphisternal. It presents the usual form, and slight sigmoid flexure, characteristic of the Chelones ; it measures one inch in length. In an Emys of the same size, the femur, besides its greater bend, is one inch and a half in length. A Chelonian cranium from Sheppey, two inches five lines in length, in the museum of Professor Bell (PI. 24, fig. 4), and a second of the same species from the same locality, two inches nine lines in length (PI. 25, figs. 1, 2, and 3), in the museum of Fred. Dixon, Esq., F.G.S., belong to the same species, and differ from the cranium of the Chelone breviceps, in the more pointed form of the muzzle, and the less rugose character of the outer surface of the bones ; they equally differ from the Chelone longiceps in the less produced, and less acute muzzle, and the more rugose surface of the bones. The parietals (7) are bounded anteriorly by a semicircular line, not by a semioval one, as in Chel. longiceps, or by an angular one, as in Chel. breviceps. The frontals (11) enter into the formation of the orbits, as in both the foregoing species. The orbits are subcircular, as in Chel. longiceps, not subrhomlwidal with the angle rounded off, as m Chel. breviceps. The postfrontals (12) are large, and forma slight projection at the back part of the supraorbital ridge. The tympanic cavity is larger in proportion than in the Chelone longiceps. The palate is traversed by a deep median, longitudinal groove, between which and the shallower grooves on the inner sides of the alveolar borders, are two well-marked, diverging, longitudinal prominences. The bony palate is longer than in Chelone breviceps, shorter than in Chel. longiceps. 24 BRITISH FOSSIL REPTILES. The symphysis of the lower jaw (PI. 14, fig. 3) is longer or deeper than 'in the Ch clone breviceps, but is convex below from side to side, and not flattened as in the Chelone planimentum. All the specimens of Chelone conv.exa, which I have been able to determine, are from the London clay of Sheppey. Chelone subcristata. Owen. Plate 15. Proceedings of the Geological Society of London, December 1, 1841, p. 5/6. Report ou British Fossil Reptiles, Trans. British Association, 1841, p. 179. The fifth species of Chelone from Sheppey, distinguishable by the characters of its carapace, approaches more nearly to the Chelone caouanna in the form of the vertebral scutes {v\ — va), which are narrower in proportion to their length, than in any of the previously described species ; but the Chelone subcristata is more conspicuously distinct by the form of the fifth and seventh neural plates (6, 8), each of which supports a short, sharp, longitudinal crest ; a similar crest is developed from the contiguous ends of the second and third neural plates (3, 4) ; the middle and posterior part of the nuchal plate (1) is raised into a convexity, as in the Chel. loiifficeps ; but not into a crest. The keeled structure of the above-cited neural plates is more marked than in the third and fifth neural plates of Chelone mydas, which are raised into a longitudinal ridge. The neural plates in the present carapace have the ordinary, narrow, elongated form of those in the true Chelones. The nuchal plate (1) has the middle of its hinder border produced backwards, instead of being emarginate, as in the Chel. brevicejjs (PL 16, fig. 1, ch). The first neural plate in the Chelone subcristata (PI. 15, 2j resembles that in the Chelone conveo:a, but is narrower in proportion to its length ; the second (3) is also quadrangular, as in Chel. convexa, but is narrower ; the third to the seventh likewise differ from those in Chel. convexa only by being narrower ; but the eighth and ninth neural plates are relatively smaller than in any of the befoi'e-described fossils, and resemble those of existing Chelones. The expanded plate is more elevated, and is bent down on each side, with the middle pai't forming an obtuse longitudinal ridge. A part of the contiguous portion of the first (jW/l) and the second {pli) costal plates are raised into a slight convex eminence on each side ; the surface of the remaining pairs of ribs is flat in the axis of the body, but they are more convex transversely to that axis, and in the direction of their own length, than in the other Chelonites. The whole outer surface of the bones of the carapace is as smooth as in the Chel. lonc/icejys and Chel. convexa. Subjoined are comparative lengths of the carapace from the first to the eighth neural plate inclusive : Ch. subcristata. Ch. breviceps. Ch. loiiyiceps. Ch. convexa. Inches Lines. Inches Lines. Inches. Lines. Inches. Lines. 74 56 59 58 CHELONIA. 25 The length of the present fossil carapace, to the tenth neural plate, inclusive, is nine inches. The breadth between the ends of the third costal plates, in a straight line, is six inches six lines. The succeeding costal plates more gradually decrease in breadth, than in the Chel. longiceps and Cliel. corwexa ; and the entire carapace more resembles in form that of the Chel. mi/das, and Chel. caouanna. The epidermal scutes are defined by deep impressions, and as wide, relatively, as in the Cltel. mydas and Chel. convcxa. The length of the second vertebral scute is two inches one line ; its breadth is two inches two lines ; the length of the fourth vertebral scute is two inches three lines ; and its breadth one inch eleven lines, and, at its posterior margin, only nine lines. This scute is narrower than in Chel. caouanna, or any of the previously described fossil species ; the outer angles are less produced than in the Chelone caouanna. Sufficient of the plastron is exposed in the present fossil to show by its narrow elongated xiphisternals (a's), and by the wide and deep notch in the outer margin of the conjoined hyosternals and hyposternals {hs andjo**), that it belongs to the marine Chelones. The xiphisternals are articulated to the hyposternals by the usual notch or gomphosis ; they are straighter and more approximated than in the Chel. mydas and Chel. caouanna. The external emargination of the plastron between the hyosternals and hyposternals, differs from that of the recent turtles in being semicircular, instead of angular ; the Chel. subcristata approaching, in this respect, to the Chel. breviceps. The shortest antero-posterior diameter of the conjoined hyosternals and hyposternals is two inches seven lines. The length of the xiphisternal is two inches six lines ; the breadth of both, across their middle part, is one inch three lines. The name proposed for this species indicates its chief distinguishing character, viz., the median interrupted carina of the carapace, which may be presumed to have been more conspicuous in the horny plates of the recent animal, than in the supporting bones of the petrified carapace. Chelone planimentum. Otven. Plates 18, 19, and 19^. Proceedings of the Geological Society of London, December, 1841, p. 5/6. Report on British Fossil Reptiles, Trans. British Association, 18-41, p. 1/8. Syn. Chelone Hakvicensis, Woodward (^l). The skull of a large Chelone (PI. 18) from the Eocene clay near Harwich, in Professor Sedgwick's collection at Cambridge, resembles, in the pointed form of the muzzle, the Chel. lonyicejjs of Sheppey ; but difi'ers in the greater convexity and breadth of the cranium (fig. 2) ; and the more abrupt declivity of its anterior contour (fig. 1), and from other Chelones by the broad expanse of the inferiorly-flattened symphysis menti (fig. 3). * Refer to fig. 3, p. 4, for these letter?. E 26 BRITISH rOSSIL REPTILES. The osseous roof of the temporal fossae, and the share contributed to that roof by the postfrontals (PI. 18, figs. 1 and 2, 12), distinguish the present, equally with the foregoing Chelonites, from the Emys {Podocnemys) eccpansa, and, a fortiori, from other genera and species of the fresh-water families {Emydidce and TrionicidcB) . In the oblique position of the orbits (fig. 2), and the diminished breadth of the interorbital space (fig. 1), the present Chelonite, however, approaches nearer to Trionyx and Emys than do the previously-described species. But the sides of the face converge more rapidly towards the muzzle. Its most marked and characteristic difference from all existing Chelones is shown by the greater antero-posterior extent, breadth, and flatness of the under part of the symphysis of the lower jaw (fig. 3), whence the specific name here given to the species. The posterior border of the symphysis is defined by a regular semicircular curve, and the rami of the jaw have completely coalesced. Since at present there is no means of identifying the well-marked species, of which the skull is here described, with the Chelonite figured in the frontispiece to Woodward's ' Synoptical Table of British Organic Remains,' and alluded to, without additional description or characters, as the Chelonia ITarvicensis, in the additions to Mr. Gray's ' Synopsis Reptihum' (p. 78, 1831); and since the extensive deposit of Eocene clay along the coast of Essex, like that at the mouth of the Thames, contains the relics of more than one species of ancient British turtles,* I prefer indicating the one here established by a name having reference to its peculiarly distinguishing character, rather than to associate arbitrarily the skull, which gives the true specific distinction, with the ill-defined carapace to which the vague name of Harvicensis has been applied; more especially as the fossil carapace to which the present skull more probably belongs, from the circumstance under which it was discovered, also presents well- marked, and readily-recognisable specific characters. This carapace (PI. 19) is also contained in the museum of Professor Sedgwick, and is understood to have formed part of the same individual turtle as the skull (PI. 1 8) on which the species, Chel. planimentum, was founded. In general form this carapace differs from that of the existing Chelones, in being less contracted and pointed posteriorly than in the Chelone mydas and CJiel caouanna, and more contracted posteriorly than in the Chel. iinhricata. In the proportion which the pleurapophyses (true ribs), bear to the superimposed costal plates, (yV4 — 8) it resembles Chelone mydas, and Chelone caouanna, more than it does the Chel. imbricata. But the pleurapophyses are more prominent and distinct from the costal plates throughout their entire length, than in the Chel. viydas or Chel. caouanna, and present an obtuse angular ridge towards the cavity of the abdomen. The five posterior pairs of ribs of the carapace {pl\ — jih) are preserved, with part * Sir C. Lyell alludes to the Chelonites of Harwich in his ' Elements of Geology :' " This formation is well seen in the neighbouring clifls of Harwich, where the nodules contain many marine shells, and sometimes the bones of Turtles." (Vol. ii, p. 337.) CHELONIA. 27 of the first three on the left side, and one of the coracoids showing the rather sudden and considerable expansion of its sternal or mesial half. The interval between the free extremities of most of the ribs, is about equal to twice and a half the breadth of each extremity ; but the interval between the seventh (jo//) and eighth (jo/s) rib, measured, like the others, at the terminal border of the costal plates, is equal to thrice the breadth of the free part of the seventh rib. In this respect the Chelone planimenttm resembles the Cliel. mydas more than it does the Chelone caoucmna, in which the interval between the free extremities of the seventh and eighth ribs is less than that between the sixth and seventh. The leno-th of the costal plate of the fourth rib is twice that of the eighth rib, as in the Chelone caouanna ; in Chel. mydas it is more than twice as long ; in Chel. imbricata it is only one third longer. The marginal pieces in the Chelone planimentum seem to have been narrow or slender in proportion to their length. The following admeasurements show that, in the large proportionate size of the head, the Chelone planimentum corresponds with the existing turtles : Inches. Lines. Length of the cranium ........ 5 6 Depth of ditto 4 Breadth of ditto 5 Length of the carapace ........ 15 6 Greatest breadth of ditto . . , . . . .13 Plates 18 and 19 satisfactorily illustrate the characteristic forms and proportions of the unique specimen in the Cambridge Museum ; the carapace is figured of its natural size, and shows its inner surface. Chelone crassicostata. Owen. Plates 20, 21, 22, 22^i, and 22-S. Testudo Plana. EOnig. ' Icones Sectiles,' PI. XVI, fig. 192? That the extinct species of Eocene turtles attained larger dimensions than those given above, is proved by a fossil skull from the Harwich clay, in the collection of Professor Bell, which gives the following dimensions : iches. Lines, 8 6 3 1 9 9 Total length of the cranium ....... Its greatest breadth ........ The antero-posterior extent of the symphysis menti . The vertical diameter of the orbit ...... do. do. of the nostril ..... This skull differs from that of the Chelone 'planimentum, in tlie minor depth of the ma.xillary bone below the orbit (compare PI. 18, fig. 1, with PI. 20, fig. 2), in the more acute and attenuated muzzle ; but especially in the minor breadth and the difi"erent configuration of the posterior margin of the synqyhysis of the lower jaw (compare PI. 18, 28 BRITISH FOSSIL REPTILES. fio-. 3, with PI. 20, fig. 3). With regard to the comparative anatomy of the bones of the skull, and the pattern of the scutation of the upper surface of the cranium, I regret that the state of the specimen in Professor Bell's collection does not permit the deduction of other distinctive characters which such parts of the cranial organization so satisfactorily afford. A great proportion of the osseous parietes is wanting ; but the cast in the hard matrix of the wide lateral cavities (12, 12), which were over-arched by the expanded postfrontal and parietal bones, indicates the prominence of the postfrontals at the upper and outer angle of the orbits. The orbits {or) appear to have been more ovate and less circular than in the Chelone planimentum ; and the sides of the orbital part of the skull do not converge so rapidly towards the muzzle, but meet at a more acute angle. That a second species of turtle, distinct from the Chelone planimentum,, has left its remains in the Harwich clay, is very decisively demonstrated by the almost complete carapace in the British Museum, the inner surface of which is represented, on the scale of six inches to a foot, in PI. 21. This carapace, both by its general contour, by the relative length of the costal plates to one another, and by their relative breadth to the adherent pleurapophyses beneath, more resembles the carapace of the Chelone imbricata than that of the other known existing species of turtle ; and, as the peculiar characters of the Chelone imhricata are exaggerated, it differs in a proportional degree from the Chelone planimentum. These characters are seen in the great breadth of the pro- minent inferior part of the ribs, and of the free extremity of the rib (/j/i— jyfe), as compared with the total breadth of the costal plate. The intervals between the free extremities, where the expanded plate terminates, are not equal to the breadth of the proper ribs ; in the Chelone imhricata they very slightly exceed the breadth of the free ends of the ribs. This character in the fossil, by which it is so markedly distinguished from the Chelone planimentum, and most other species, has suggested the name Chelone crassi- costata, or thick-ribbed turtle, which is proposed for the present species. The last pair of ribs of the carapace (PI. 21, ph) are remarkably short and thick, and are curved backwards on each side the broad terminal neural plates which they almost touch. In this character the Chel. crassicostata resembles the Chel. imbricata, and differs from the Chel. caouanna (fig. 2, p. 3), and from Chel. mydas. The subequality of length of the costal plates is another character by which the Chel. crassicostata resembles the Chel. imbricata, and differs from the Chel. mi/clas, the Chel. caouanna, as well as from the Chel. planimentum. In PI. 21, as in the other figures, ch is the nuchal plate, ph the first rib of the carapace (the second free pleurapoph)^sis or vertebral rib), ph to j'Vs the remaining ribs of the carapace and costal plates ; sg, siO, and pi/ are the terminal neural plates and pygal plate, which, like the nuchal plate, are developed in the substance of the integument, without becoming attached to the subjacent spinous processes of the vertebrae. The debris of the neural arches of the intermediate eight vertebrse of the CHELONIA. 29 carapace are preserved in the interspaces of the beginnings of the ribs and costal plates in this beautiful Chelonite. It forms part of the Fossil Collection in the British Museum. A carapace of a smaller individual of Chehne crassicostata, from the Harwich coast, vi'ith the character of the broad and inwardly-prominent ribs strongly marked, is likewise preserv^ed in the choice collection of my esteemed friend Professor Bell. One of the hyosternal bones, inclosed in the same nodule of clay, testifies to the partial ossification of the plastron in this species by its coarsely-dentated border ; and, at the same time, shows a specific peculiarity by the convexity of that surface which was turned towards the cavity of the thoracic-abdominal case. On the moiety of the nodule containing the carapace and exposing its under surface, the slender rudimental rib of the proper first dorsal vertebrae is preserved, in connexion with the first expanded rib of the carapace. Besides the specimen of Chehne crassicostata from Harwich, figured in PL 21, there is a mutilated carapace of a young Chehne, from the same locality, in the British Museum. This specimen exhibits the inner side of the carapace, with the heads, and part of the expanded bodies, of four pairs of ribs, which indicate its specific agreement with the foregoing specimen, and demonstrate unequivocally its title to rank with the marine turtles. It is figured in Mr. Koenig's ' Icoues Sectiles'' (pi. xvi, fig. 192), under the name of Testudo plana. A rare Chelonite from the hard Eocene clay apparently of Harwich, in the collection of my friend Frederick Dixon, Esq., F.G.S., of Worthing, shows the impressions from the under surface of the carapace, and also an instructive part of the under surface of the plastron itself. (PI. 22.) The proportions and degree of convexity of the under surface of the costal plates of the carapace (yV, pi) correspond with those parts in the Chehne crassicostata. The remains of the plastron include a great portion of the left hyosternal {hs), left hyposternal {ps), and left xiphisternal {xs) ; the latter is articulated to the hyposternal by a notch, receiving a toothed process, and, reciprocally, near the upper part of a long oblique harmonia, between the outer border of the hinder angle of the h3iiosternal and the inner border of the upper half of the xiphisternal. The hyosternal is concave lengthwise, and is convex across on its under surface ; the transverse linear impression, dividing the pectoral and abdominal scutes, crosses near its posterior border. The degree of concavity of the outer surface of this bone corresponds with the convexity of the upper and inner surface of the same bone in the specimen of the Chehne crassicostata from Harwich, in the Museum of Professor Bell ; and it concurs with the characters of the costal plates in proving the present Chelonite to be of the same species. Impressions of the toothed mesial margin of the right hyosternal remain, and part of the toothed margin of the left hyposternal. 30 BRITISH FOSSIL REPTILES. The right coracoid (52) is exposed by the removal of the right hyosternal ; it differs in form from that preserved in the large specimen of Chelone planimentum, in Professor Sedgwick's Museum, in expanding less suddenly at its sternal end, as compared with the coracoid of the Chelone mydas, or with that of the Chelone caouanna, which is somewhat broader than in the CIlcI. mydas ; the coracoid of the Chel. crassicostafa agrees with that of the Chel. planimentum in the greater degree of its expansion. At the anterior fractured surface of Mr. DLxon's Chelonite, the long and slender columnar or rib-like scapula, is shown, extending from the under part of the head of the second costal rib downwards and outwards, for an extent of two inches, and then sending its acromial or clavicular prolongation at the usual open angle downwards and inwards to rest upon the episternal. The proportions of these parts of the scapular arch are quite those which characterise the genus Chelone, but they do not supply such marks of specific distinction as the coracoid element does. Chelone declivis. Owen. Plate 23. The extinct turtle represented by this specimen, and indicated by the above terra, bears the same relation to the Chelone convexa, which the Chelone lonyleeps* does to the Chelone latiscutata ;t that is, it has the same general characters of the petrified parts of the carapace, but diff"ers in the narrower proportions of the vertebral scutes {v\ — v\), and the more open angle at which their two lateral borders meet ; the vertebral angles of the costal scutes being correspondingly less acute. The specimen is from the Eocene deposits of Bognor, Sussex, and is preserv^ed in the collection of Frederick DLxon, Esq. It consists of the seven anterior neural plates, and the corresponding seven pairs of costal plates (PI. 23, fig. 1), those of the right side having been broken away from their attachments to the neural plates, and bent upon the rest of the carapace at an acute angle with some slight separation of the sutures of the costal plates (fig. 2). The neural plates correspond in general form with those of the Chelone convexa, the hind ones being rather broader ; the first (.si) is crossed at its middle part by the impression dividing the first (^m) from the second (vi) vertebral scute ; the second neural plate (s'l) is an oblong four-sided one, with both ends of equal breadth. The third neural plate, S3, resumes the hexagonal figure with the broadest end, and two shortest sides at the fore part ; and is crossed in its lower half by the impression dividing the second, VI, from the third vertebral scute, t'3. The fifth neural plate (,s^5) is crossed by the next transverse impression nearer its lower border. The sixth and seventh neural j^lates retain the same form and proportions as in the Chelone convexa, except a somewhat * Proceedings of tlie Geological Society of London, December 1, 1841, p. 572. t Ibid., p. 574. CHELONIA. 31 greater breadth, and have not their antero-lateral borders increased in length, as in the Chelone longiceps. The dechnation of the ribs from the neural plates, gives a greater degree of steepness to the sides of the carapace than in the Chelone convexa, and the impressions of the scutes have equal depth and breadth. The chief difference indicative of specific distinctions, lies in the form of those impressions ; and the question is, whether, in the progress of growth which makes the longitudinal extent of two of the vertebral scutes in one specimen nearly equal to three, in another, so great a change could be effected in their shape as is shown in the specimen of Chelone convexa ; in which it will be seen that the second vertebral scute (PI. 14, fig. 1), though one third shorter than in Chel. declivis (PI. 23, V2), is of the same breadth as that in the larger specimen, and that the rest differ in the same remarkable degree. Fig. 3 shows the characteristic declivity of the sides of the carapace in the present species. Chelone trigoniceps. Oicen. Plate 25, figs. 4, 5, and 6. More than one of the old tertiary turtles {Chelone) are remarkable for the longitudinal extent or depth of the symphysis of the lower jaw. The turtles from the Eocene clay at Harwich have this character so strongly developed and the under surface of the symphysis so flattened, especially in one of the species (PI. 18), as to have suggested the " nomen triv'mle" planmentmn for it. The Chelone longiceps (PI. 12), if we may judge by the length of the upper jaw and bony palate, must have had a corresponding extent of the symphysis of the under jaw ; and we may infer the same peculiarity from the straight alveolar borders of the maxillaries and their acute convergence towards the premaxillary bones in an allied species, Chelone trigoniceps, which I have described and figured in the Appendix to Mr. Dixon's work on the 'Fossils of Sussex,' from a specimen which is in the collection of G. A. Coombe, Esq., and which was obtained from the Eocene clay at Bracklesham. Amongst the Chelonites which Mr. Dixon has obtained from the same formation and locality, ai'e portions of the fore part of the lower jaw of four individuals of the genus Chelone, all exhibiting the characters of the pointed form and great depth of the symphysis. One of these specimens (PI. 18, figs. 5 and 6) agrees so closely in size and shape with the fore part of the upper jaw of the Chelone trif/oniceps (fig. 4) — fits, in fact, so exactly within the alveolar border, and so closely resembles that specimen in texture and colour, that, coming from the same formation and locality, and being obtained by the same collectors, I strongly suspect it to belong to the same species of Chelone, if not to the same individual. The known recent Chelones differ among themselves in the shape and extent of the bony symphysis of the lower jaw. Both the Chelone imbricafa, and Chelone caouanna 32 BRITISH FOSSIL REPTILES. have this part deeper and more pointed than the Chcl. mydas, but neither species has the symphysis so depressed or so slightly convex below as it is in the Bracklesham CJielones. These also differ amongst themselves in this respect. The symphysis (figs. 5, 6, 11) which I have referred to the Chelone iriyomcep><, is the broadest and flattest ; at its back part (fig. 7) it shows a deep and broad genio-hyoid groove ; this is reduced to a transversely oblong foramen in Chelone mydas. The second species from Bracklesham, is indicated by the maxillary symphysis (fig. 9), the sides of which meet at a more acute angle, and it is narrower in proportion to its length, is more convex below, and more concave above, with the alveolar borders a little more raised, and the middle line less raised than in Chelone trigoniceps. In this respect it is intermediate between the Chelone imbricata, -where the upper surface of the symphysis is more concave, and the Chelone caouanna, where it is flatter than in the Chelone triyoniceps. The fossil symphysis under notice, has also a smooth, transverse, genio-hyoid groove at its back part. It accords so closely in form with the end of the upper jaw of the Chelone lonyiceps, from Sheppey, that I refer it provisionally to that species. Two other specimens of the symphysis of the lower jaw (figs. 8, 10), of rather larger size, appear to belong to the same species as that referred to the Chel. lonyiceps, by the characters of the concavity of the upper surface, the convexity of the lower surface, and the degree of convergence of the sides or borders of the symphysis. The larger of the two shows the genio-hyoid groove, and the nearly vertical outer side of the jaw, opposite the back part of the symphysis, and this shows no impression of the smooth fossa receiving the insertion of the biting muscles, whereas, in the Chelone trigoniceps, fig. 11, that fossa extends to the same transverse line or parallel with the back part of the symphysis. The very rare and interesting Chelonite in Mr. Coombe's museum (fig. 4) was the first portion of the cranium of a reptile of this order that I had seen from the Eocene deposits at Bracklesham. It includes the bones forming the roof of the mouth, with portions of the bony nostrils and orbits, and the tympanic pedicles. The extremity of the upper jaw is broken off, but the straight converging alveolar borders clearly indicate the muzzle to have been pointed, as in the Chelone longiceps of Sheppey; and the muzzle being shorter, the form of the skull has more nearly approached that of a right-angled triangle. The whole cranium is broader and shorter, and the tympanic pedicles wider apart. The middle line of the palate developes a somewhat stronger ridge ; the orbits were relatively larger and advanced near to the muzzle : the malar bones are more protuberant behind the orbits, and their external surface inclines inwards as it descends from behind and below the orbit, to form the lower border of the zygoma, which it does not do in the Chelone longicejis. The upper surface of the fossil shows the palatines rising to form the vomer at the middle line, and the two small subcircular vacuities (occupied by membrane in the CHELONIA. ,. 33 recent skull) between the palatines, prefrontals, and niaxillaries ; the anterior border of the temporal fossa, formed by the malar and pterygoid, is entire on one side, and shows that that vacuity was as broad as it is long. The olfactory excavations in the maxillaries are deep. The articular surface of the tympanic pedicles closely accords with those of recent Chelones. The very regular triangular form of the skull indicated by this fragment, has induced me to propose the name of Chelone trigoniccjis for the species. Chelone cuneiceps. Owen. Plate 11. One of the most complete and instructive crania of the fossil turtles of our Eocene deposits is the subject of PI. 1 1, the opportunity of describing and figuring which has been kindly afforded me by J. Toulmin Smith, Esq., F.G.S., of whose cabinet it forms part, and by whose skilful manipulation its variously configurated exterior has been disencumbered of the hard adherent clay. From the Chelone breviceps this specimen differs by its more prolonged and pointed muzzle ; by the more sudden and sloping declivity of the prefrontal part of the cranium (fig. I, 14) ; by the minor degree of rugosity of the surface of the bones ; and by the different disposition of the superincumbent horny scutella, which is indicated by their impressions. In the general arrangement of these impressions it accords better with the cranium of the Chelone lonpcejjs ; but differs in the greater breadth of the skull as compared with its length ; in the minor extent of the bony palate (fig. 3, 20, 21), the more advanced position of the posterior nostrils, and the greater length of the pterygoids (24). From the Chelone convexa it differs, in the greater relative breadth and flatness of the frontal bones, and of the whole intcrorbital platform (fig. 2, ii), in the downward slope of that part of the cranial profile, and in the more prominent convexities of the palatal pi'ocesses of the maxillaries. From the Chelone planivienfum it differs also, by the broader prefrontal part of the intcrorbital space, as compared with the transverse diameter of the back part of the skull ; by the minor degree in which the frontal enters into the formation of the upper rim of the orbits ; by the minor depth of the suborbital part of the maxillary and malar bones, and by a very different arrangement of the supracranial horny scutella. The basi-occipital (PI. 11, figs. 3 and 4) is remarkable for the strong development of the tubercles for the insertion of the strong " recti capitis antici," and for the depth of the median groove between them ; the semicircular fossa in front of these processes is bounded by a well-developed basi-sphenoidal ridge (5), the curve of which is deejjer than in Chcl. longiceps, but shallower than in Chel. breviceps. In the Chel. caoiianna, in which the basi-occipital tuberosities are better developed than in the Chel. hnhricata or Chel. mi/das, they are bounded anteriorly by an angular or chevron-shaped ridge of the basi-sphenoid. The exoccipitals (2) form the usual share of the trilobate occipital F 34 BRITISH FOSSIL REPTILES. condyle characteristic of the Chelonia. The paroccipitals (4) project backwards to a little beyond the posterior plane of the condyle, indicating an affinity to the Trionycidce. The inferior surface of the part of the tympanic to which they unite is concave. The parietals (fig. 2, 7) form together a large semielliptic, almost flattened, platform, relatively broader than in Chel. viydas, not convex, as in Chel. caouanna ; not in- dented by the mastoids, as in the Chel. hnpceps, and not forming an angle between the frontals and postfrontals, as in the Chel. breviceps. The frontals (11) together form a pentagon, with the longest margin joining the parietals, the next in length con- verging to a point between the prefrontals, and the shortest borders joining the post- frontals. The postfrontals (12) and prefrontals (14) almost meet above the orbits, and exclude the frontals from entering into the formation of its superior border. The Chel. mi/das comes nearest to the Chel. cuneiceps in this particular ; whilst in the Chel. imbricata the frontals enter as largely into the formation of the upper border of the orbit as they do in the Chel. breviceps, Chel. longicepts, and Chel. coiwexa. The precise form of the termination of the prefrontonasals, the maxillaries, and premaxillaries cannot be determined in the present specimen ; fortunately, the fracture of the anterior extremity of the skull has not extended to that of the bony palate. If this be bounded by a transverse line behind, drawn across the anterior border of the temporal fossse, the space included forms a right-angled triangle, and includes the whole of the posterior nostrils. In the Chel. longiceps the similarly defined space has the base shorter than the converging sides, and the posterior nasal aperture is behind the transverse line. The bony palate, also, of Chel. cuneiceps, instead of being pretty uniformly concave and even, as in Chel. longicep)s and Chel. caouanna, is raised on each side between the middle line and the marginal alveolar plate into two convexities, as in Chel. mydas and Chel. imbricata ; but the most prominent part of the palatal convexities (figs. 3 and 4, 21) is obtuse in Chel. cuneiceps, not sharp or angular, as in Chel. wydas and Chel. imbricata. The palatal part of the vomer (13) forms the median longitudinal groove dividing the convexities, which arc formed by the palatal processes of the maxillary bones. The small part of the alveolar border of the maxillary which is entire terminates in a sharp edge, extending about four and a half lines below the level of the palate. The ridge of the palatines, which forms the anterior boundary of the posterior nostril, is not produced or bent below the level of the bony palate, as in Chel. caouanna, and as it is, although in a minor degree, in Chel. mydas ; and there is not that concavity between it and the oblique palatal tuberosity which exists in the Chel. mydas and Chel. imbricata. The pterygoids are more deeply (semicircularly) emarginate laterally than in any of the existing species of Chelones, and they are shorter in proportion to their breadth ; they bound internally the lower apertures of the temporal fossse, which are broader than they are long ; in all the existing Chelones the opposite proportions prevail, CHELONIA. 35 and in Clicl. wibricata especially the homologous apertures are twice as long as they are broad. Tlic pterygoids, in the CJteL cunekqjs, develope a sharp ridge along their median suture ; and short but well-defined processes at their anterior and outer angles. The channel or concavity upon the under part of the diverging portion of the pterygoid conducts obliquely into the temporal fossae in the Chd. my das ; in Chel. cuneiceps it leads directly forwards upon the under surface of the anterior part of the pterygoids exclusively, as in the Chel. imhricata and Chd. caouanna. In the Cliel. mydas the malar approaches the mastoid very closely, and sometimes touches it by the posterior angle, thus separating the squamosal from the postfrontal ; the extent of the unioiv between the squamosal and postfrontal is also shorter in the Chel. caouanna than in the Chel. imhricata. In the extent of that union (between 12 and 27) the Chel. cuneiceps resembles the Chel. imhricata, as do likewise the Chel. hreviceps and Chel. loiiyiceps. But the Chel. cuneiceps diflFers from all the recent species in the form of the squamosal (27), which is bent upon itself, forming a slightly curved linear eminence, where the lower and smoother part of the bone is bent, and, as it were, pressed inwards towards the tympanic (28), against which it abuts. This modification is natural, not the effect of accidental pressure upon the fossil. The lower border of the malar (2G), which intervenes between the maxillary and squamosal, is sharp but convex, as in Chel. caouanna, not concave as in Chel. mydas, nor nearly straight, as in Chel. imhricata. But the concave curve of the inferior margin of the squamosal (27) most resembles that in Chel. imhricata. The antero-posterior extent of the mastoid (s) is less proportionally than in any of the recent Chelones, and it forms a smaller share of the upper border of the large meatus auditorius. The articular part of the tympanic descends below the squamosal further than in the i-ecent turtles ; and its articular surface is more convex at its outer half, and more concave at its inner half; Chel. imhricata makes the nearest approach to the fossil in this respect. In the Chel. mydas and Chel. caouanna the articular surface is nearly flat. As the supracranial scutella have left imusually deep and well-marked impressions on this fossil skull, I have reserved their description, and the comparison of their different forms and proportions in the sevei'al fossil species, to this place. Three scutella occupy the median line of the upper surface of the cranium in the present species of Chelone, which, from the absence of any impression along the frontal and sagittal sutures, appear to have been single and symmetrical. The anterior and smallest answers to the " frontal" scute (fig. 2, //•) ; the next in size and position to the " sincipital" scute {sy) ; the hindmost and largest answers to the " occipital" scute {oc), which is usually divided, and forms a pair in existing Chelones. The frontal scute is long, narrow, hexagonal, broadest across the antero-lateral angles, from which the impressions extend outwards to the supraorbital margin, which divide the " fronto-nasal" scute from the " supraorbital" scute {oh). The sincipital scute is bounded on each side by a sigmoid curve, and both before 36 BRITISH FOSSIL REPTILES. and behind by an entering angle ; it is broadest behind, and from the middle of the lateral border proceeds the transverse impression towards the back part of the orbit, which divides the " supraorbital" scute {ob) from the " parietal" scute {pa). The occipital scute is bounded laterally by straight lines, which slightly diverge as they extend back- wards : there is no trace of an interoccipital scute. The parietal {pa) scute is the largest ; impressions of five of its borders are preserved in the present fossil : the two exterior ones meet at an obtuse angle, a little above the middle of the meatus auditorius externus ; the antero-external border uniting with the postorbital scute {jjo) ; the postero-external border with the external occipital scute {eo). In the Clielone brevicejys (PL 1 7 A, fig. 2) the frontal scute is relatively larger than in the Clielone cimciceps, and is nearly as broad as long. The sincipital scute is bounded laterally by two straight lines meeting at a very open angle, from which the transverse impression extends outwards between the supraorbital and parietal scutes. The straight lines bounding the sides of the occipital scute diverge from each other as they extend backwards more than they do in the C/ielone cimcicejjs. In the Clielone lonc/iceps (PI. 1 2) a still more different pattern of the supracranial scuta- tion is presented. The occipital scutes {oc) are separated by an intervening interoccipital scute {io). The lateral borders of the sincipital scute are each bounded by three lines and two angles ; the antero-lateral and postero-lateral angles being curved with the concavity outwards ; and the transverse impression dividing the supraorbital scute {oh) from the parietal scute {pa), proceeds from the middle of the intervening straight border of the parietal. The frontal scute {fr) is long and narrow, broadest behind, with its lateral borders gradually converging to a point anteriorly ; the impression dividing the supraorbital {oh) from the frontonasal scute {fn) proceeds from the middle of that lateral border. Neither the division between the frontal and sincipital, nor that between the sincipital and interoccipital scutes are well marked. The Clielone convexa (PI. 24, fig. 4), like the Clielone lonpceps, has an interoccipital scute {io), and the sincipital scute {sif) has its sides bounded by three lines, of which the posterior one is curved with its concavity towards the occipital scute (oe), and so directed as to appear to form part of the posterior rather than the lateral border ; the other two lines completing the lateral border and converging forwards, are divided or defined by a slight angle, from which the transverse impression proceeds outwards, which divides the supraorbital {oh) from the parietal {pa) scutes. The frontal scute (//•) is a small hexagon, relatively \\\A.ev than in Cliel. longiceps or Cliel. cuneiceps. The impression dividing the supraorbital {oh) from the frontonasal {fn) scutes proceeds from the angle between the lateral and anterior sides of the frontal scute. The Clielone planimentum (PI. 18) is peculiar, and differs fi-om all the foregoing species by the forward extension of the occipital scutes which join the supraorbital scutes, and thus divide the sincipital scute {si/) from the parietal scute {pa) ; the sincipital scute CHELONIA. 37 is correspondingly encroached upon, as it were, and narrowed, its broadest part being nearer the anterior end, at the angle between its two straight lateral borders, from which angle the impression extends outwards that divides the occipital from the supra- orbital scute. The frontal scute (/;•) is small and narrow, and the large supraoi-bital scutes meet in front of it at the middle line. They appear to be divided from the orbits by the encroachment of palpebral scutes (/;/) upon the supraorbitary border. There appears to have been an interoccipital scute in the Chel. jjlanimentum, as in the Chel. lon^icejjs and Chel. convexa. Amongst existing Chelones the interoccipital scute is constant only in the Cliel. caouanna — the loggerhead of Catesby and Brown ; but the sincipital scute in this species is vastly larger in proportion than in any of the fossils above described ; and it is further distinguished by the peculiar division of the supraorbital and parietal scutes. In the hawks-bill turtle {Chel. imhricata), the supracranial scutes leave as well- marked indentations upon the bones of the cranium as are seen in most of the fossil turtles, but the supraorbital scute is proportionably larger than in any of these, and the proportions and forms of all the other scutes are different. There are, also, two nasal scutes divided by a transverse groove from the frontonasals, which groove I have not yet met with in the corresponding part of any of the fossil Chelonian crania. The skull of the Chelone cimeiceps, here described, is from the London clay of Sheppy. Chelone subcarinata. Bell. Plate 10. The resemblance of this species to Chelone subcristata (p. 24, PL 15) is so con- siderable, that it has not been without some hesitation that I have ventui'ed to describe it as distinct. There are, however, certain characters by which it may be distinguished, and those of sufficient importance to be considered as specific. On comparing it with recent species, and even with most of the fossil ones from the same locality, there is a remarkable evenness in the arch of the carapace, which, with the exception of a slight carina on some of the posterior neural plates, to be hereafter mentioned, forms nearly a perfect arc of a circle, from the extremity of the costal plate of the one side to that of the other, without that flattening of the side which is seen in most other species. The nuchal plate (PI. 10, fig. 1, ch) has the posterior margin arched, and there is a short median process which goes to join the first neural plate (*l), in which respect it agrees with Chel. lo)i(/ice2)s and with Chel. subcristata. This process is emarginate, to receive a slight triangular projection of the anterior margin of that plate. The first neural plate {s\) forms a parallelogram, the sides not being interrupted by any costal suture ; the posterior suture of the first costal plate (jo/l) extending to the second neural plate (6'2). In this circumstance it differs from Chel. subcristata, lofipcejjs, and convexa, and agrees with Chel. breviceps. This, however, may possibly be a variable character here, as 38 BRITISH FOSSIL REPTILES. it is in Chel. loncjiceps ; in one specimen of which, now before us, the articulation of the first costal plate was with the anterior part of the second, instead of the posterior part of the first, neural plate ; in other words, the first neural plate was the isolated one instead of the second. The remaining neural plates are hexagonal, becoming almost regularly shorter to the eighth ; the lateral angles meeting the costal sutures being nearly at the same distance from the anterior margin in each, and in no one at all approaching a regular equilateral hexagon, as in many of the neural plates in C/iel. breviceps. The first three, and the anterior half of the fourth neural plates are flat; but on the posterior half of the fourth commences a low carina, which becomes highest on the posterior half of the sixth (*g), and anterior half of the seventh {&-). It thus differs from Chel. subcristata, in which there is a distinct, short, sharp, longi- tudinal crest (.si) on the fifth and seventh neural plates, " and a similar crest is developed on the contiguous ends of the second and third neural plates." The ninth and tenth neural plates are wanting in the only specimen I have seen of the Chel. subcarinata. The first costal plate is flat [ph), but the remaining ones, to the seventh inclusive, are slightly hollowed along the middle, being raised towards the anterior and posterior margins, where they are articulated to the contiguous ones. The w'hole surface of the bones of the carapace is less smooth than in most other fossil species, and conspicuously less so than in Chel. subcristata. In describing the forms of the vertebral scutes, (n — va), and of the costal ones as depending upon them, it is necessary, in order to arrive at any satisfactory comparison between these parts in difl'erent species, to bear in mind that a great change takes place in their outline during the growth of the animal ; and that a vertebral scute, w^hich, in a younger individual, has the middle of its outer margin exceedingly extended, so as to form a very acute angle, where the lateral margin of the costal scute joins it, and thus rendering it twice as broad as it is long, may in more advanced age have that angle verv open, and having increased greatly in length, and scarcely at all in breadth from angle to angle, the length becomes greater than the breadth. Allowing, however, for this fact, there are doubtless considerable variations in this respect according to the difl'erent species, which are permanent and well marked. The first vertebral scute {v\) in the present species is quadrilateral, broader anteriorly ; the second and third {v2, V3) hexagonal, with the outer margins slightly waved, somewhat broader in the middle at the angles than at the anterior and posterior margins, the comparative breadth at that part being rather greater than in the corresponding scutes of Chel. svbcrisfata, and much less so than in Chel. convexa, Chel. brevicejis, or Chel. longiceps. The fourth vertebral scute (r4) is also hexagonal, but the portion posterior to the lateral angles is narrowed and produced backwards. The last of the series is fan-shaped. The outline of the costal scutes follows of course that of the vertebral ones. The plastron, in the specimen from which this description is taken (PI. 10, fig. 2), is more perfect than in that of almost any other fossil Chelonian I have seen. It CHELONIA. 39 agrees in its general form with that of Chel. subcristata, but is less extensive, as regards its bony surface, than in Chel. loiifflceps or even than in Chd. breoiceps. The entosternal bone (s) is somewhat wedge-shaped, with the anterior margin triangular, and a short winged process on each side of the anterior third of the bone extending outwards and backwards. The posterior extremity of the bone, and the winged processes are dentate. The episternals {es) are aliform, tending backwards and outwards, and inclosing between them the head of the entosternal (*), and the anterior processes of the hyosternal bones [Its). The latter have the anterior processes extending forwards on each side of the entosternal, approximating at their extremity the aliform processes of that bone. The median or internal processes nearly meet on the median line, and the den- tations are deep but slender ; each hyposternal {ps) unites similarly with its fellow, and the posterior process extends backwards, in a long, narrow, triangular piece, uniting with the xiphisternal {xs), which latter forms a very elongated rhomb, the breadth of which is scarcely one fourth of its length, which in the present specimen is no less than two inches six lines. This form, with the elongation and narrowness of the posterior process of the hyposternal, gives to the hinder portion of the plastron in this species a narrower and more elongated outline than we find in almost any other; an approach to which is, however, indicated in the imperfect specimen of Chel. subcristata figured in Plate 15. The external notch, between the external process of the hyosternal and hyposternal, is deep and rounded. The central interspace is nearly quadrate, and about half as long again as it is broad. Inches. Liues. Lengtli of the carapace as far as it is preserved ... 9 5 Breadth of ditto from the extremity of the third costal plate on one side to that on the other ...... 7 4 Ditto, following the convexity of the carapace ....!) 3 Length of plastron from the anterior margin of the episternal to the extremity of the xiphisternal .... 8 4 Breadth of ditto across the hyosternals ..... 7 The only specimen of this species which I have seen is from Sheppy, and is in the fine collection of J. S. Bowerbank, Esq., F.R.S. T. B. SUPPLEMENTAL REMARKS ON THE TURTLES FROM THE LONDON CLAY AT HARWICH. In the progress of the works now carried on in a part of the Harwich cUfFs, with a view to the acquisition of the remains of the animal tissues and bone-eartli which form the nodules that are ground up and used as manure, many remains of the Chelonian reptiles which formerly frequented the seas from which those Eocene tertiary strata have been deposited have been discovered. Mr. Colchester, of Little Oakley, Essex, who carries on large works of this kind for the " Fossil Guano," as it is termed, has transmitted to me a number of the nodules in question. The most intelligible and instructive of these I have marked from 1 to 10 consecutively, and shall notice them here in the same order. No. I. CJtelone planimentum. This is the half of an oval nodule of petrified clay, 20 inches in length, by 17 inches in breadth, exposing an in-egular group of disarticulated bones of the carapace and other parts of the skeleton. The species is determined by a fragment of one of the costal plates with the connate rib. The plate measures 2\ inches in breadth, the rib 8 lines, and forms the usual partial prominence from the even surface of the under part of the costal plate. Almost the whole of the very broad but short nuchal plate is recognisable : it measures 6 inches in transverse diameter, and only I5 inch in antero-posterior diameter. Part of the hyosternal bones, and the impression of the humerus are recognisable. No. 2 is the half of a nodule, 20 inches in length and 17 inches in breadth, exposing part of the plastron, and some other bones of the skeleton of the CIicJ. j^Iani- mentum. It shows well the natural form of the under and outer part of the hyposternal bone, which is much more deeply excavated than in the Chel. crassicosfafa ; the lower portion of the bone is narrower in proportion to its length, and the xiphisternals are also in proportion longer and narrower than in that species. No. 3. Clidone 2ilanimenhm . The half of an oval nodule, 17 inches in length and 13 inches in breadth. The fractured side exposing a cast of the inner surface of the carapace, which measures in length from the nuchal to the tenth neural plate inclusive 13^ inches ; and in breadth, across the third pair of costal plates from one end of the projecting rib to that of the opposite side, 1 1 inches. The anterior contour of the CHELONIA. 41 carapace is well shown in this nodule, the marginal plates which join the nuchal plate being preserved. The free extremity of the rib attached to the third costal plate projects 1 inch 9 lines from that plate, and measures 7 lines in breadth, where it becomes free ; the breadth of the plate being nearly 2 inches. The transverse curve of the carapace is shown by this specimen to be much less than in the Chel. crassicostata. No. 4. Cliel. 2^lcinhnentum. The nodule shows partly a cast of the outer surface of the carapace, with part of the carapace itself. The outer angles of the third and fourth vertebral scutes are here seen with the inner angle of the third costal scute. The outer angles of the vertebral scutes are more prominent than in Chel. declivis, Chel. subcristata, Chel. subcarinata, Chel. convexa, or Chel. longiceps ; they resemble most those in Chel. breviceps. The breadth of the third costal scute is 4 inches. The characteristic angular ridge, formed by the narrow connate rib, where it projects from the lower surface of the costal plate, is well shown in this specimen. No. 5. A nodule showing a cast of the under surface of the carapace seen from above, apparently of the Chel. planivientum. No. 6. A nodule, 10 inches long by 9 inches broad, showing a still more imperfect cast of the under surface of the carapace, of apparently a younger specimen of the Chel. planimentum. No. 7. A fragment of a nodule showing the outer dentated extremity of the left hyosternal of the Chel. pilunimentum. No. 8. A portion of a nodule, with part of the carapace of the Chel. plani- mentum, showing the second to the seventh neural plates inclusive, and portions of the second to the seventh costal plates of the right side, with more or less of their bony substance broken away, exposing their coarse fibrous character, the fibres diverging on each side from the subjacent rib, as they extend obliquely towards the periphery of the carapace. The third neural plate is 2 inches 3 lines in length and 1 inch in breadth ; it is crossed at its middle part by a moderately broad and deep channel, indicating the junction of the second with the third vertebral scute. The third neural plate is hexagonal ; the two shortest sides being formed by the truncation of the contiguous angles of the second costal plates bending down a little to articulate with them. The fourth neural plate is 2 inches 6 lines in length, and 1 inch 4 lines across the broadest part. The anterior surface is concave, the posterior convex ; the two longest sides converge towards the posterior surface, and are straight. The fifth and sixth neural plates progressively decrease in length, without a proportionate decrease in breadth. The breadth of the fourth costal plate is 2 inches 3 lines at its peripheral extremity ; its length is 6 inches ; the rib projects 2 inches beyond it. The upper 42 BRITISH FOSSIL REPTILES. surface of the neural and costal plates is so minutely fibrous or striated as to seem at first sight almost smooth. The upper surface of the costal plate seems naturally to be slightly concave in the direction of the axis of the carapace, but not so much as in Chel. crassicostata, and the rib is much bent lengthwise. No. 9. Chelone crassicontata (PI. 22 A). This instructive specimen is contained in a subspherical nodule, 13 inches long by 12 inches broad, exposing a large proportion of the outer surface of tlie carapace, with more than one half of the circle formed by the marginal plates {mi—jiij). The carapace has been fractured, and the ribs of the left side dislocated and pressed down below those of the right. The third {ph) to the eighth {ph) costal plates inclusive are present on the left side; the fifth to the eighth on the right side, and the neural plates from the fourtli to the pygal plate {py) inclusive. The fourth, fifth, and sixth neural plates are hexagonal, with the anterolateral sides shortest, and chiefly remarkable for their great breadth in proportion to their length. The seventh and eighth are small, and more regularly hexagonal. The ninth is a broad sub- crescentic plate, with the broad concave side backwards, and the space between this and the pygal plate is filled up by an equally broad but pentagonal neural plate. The length of the ninth and tenth neural plates, with the pygal plate inclusive, is 2 inches 9 lines. The pygal plate is subquadrangular and broadest behind, where it is slightly emarginate. The length of the fourth to the eighth neural plate inclusive is 3 inches 8 lines. The upper surface of the bones of the carapace is almost smooth. That of the costal plates is chiefly remarkable for its concavity transversely, or in the direction of the axis of the carapace, which is to a greater degree than in the Clieh suhcristata or CheL longiceps ; the lines of the sutural union of these plates with each other forming so many ridges across the sides of the carapace. The degree of curvature or convexity in the direction of the length of the costal plate is much greater than in the Cliel planimentum. The length of the third costal plate is 3^ inches, its breadth at the outer extremity, 1 inch 4 lines ; the breadth of the rib where it projects beyond it is 9 lines. The margin of the plate attached to that rib is 1 inch 4 lines in length, and 8 inches in breadth. The margin of the plates gradually increases in breadth towards the posterior part of the carapace, the one joining the pygal plate being 1 inch 2 lines in breadth. The general form of the carapace of the Ckel. crassicostata is shown by the present specimen to have been that of a full oval, with a gently festooned border, not pointed behind. No. 10. Chelone crassicostata (PI. 22B.) A still more remarkable example of this species was kindly transmitted to me by the Rev. S. N. Bull, M.A., of Harwich, of which a figure is given in PI. 22B. When it first came into my hands it was an unpromising semioval nodule, 10 inches in length by 7 inches in breadth, presenting on its convex surface portions of the posterior neural and costal plates, with their external surface entire ; but no trace of plastron on the flattened side. The degree of convexity formed by the costal plates equalled that of the CHELONIA. 43 most dome-shaped tortoise. The flatter surface of the nodule was shghtly convex, which I thought might arise from a layer of petrified clay adhering to the plastron. A portion of the cranium was indicated at the produced angle of the nodule. To ascertain whether this remarkable degree of convexity of the carapace, both length'wise and transversely, was natural, I had the matrix carefully removed, with the permission of the owner of the specimen, and the same was done on the opposite side, with a view to expose the plastron. Instead of finding a plane plastron where it was expected, in its natural horizontal position, it was found to have been crushed inwards, as repre- sented in fig. 2, by the pressure of a hard petrified mass as big as a paving-stone, which had been forced in upon this part of the body of the turtle whilst in a decom- posing state ; and when finally lodged in the clay, the carapace and plastron, as they became dislocated, had become more or less moulded upon it ; and thus was produced the convexity which originally attracted my attention. In the breadth of the connate rib, as compared with that of the costal plate, in the extent of the free extremity of the rib, in the degree of concavity of the upper surface of the costal plate and the curvature lengthwise, the distinctive characters of the Chel. crassicostata are well show'n. The same characters are likewise presented by the parts of the plastron, as in the breadth of the xiphisternals (MJoES>-i''™"p<'p''y=>s- artery.' The names of the vertebral elements parapcphys,s.----'' ^\^V^ ^^"'^^' ^^^^^ usually dcveloped from distinct XV/y ■■•--ha^inapophyB.s. ceutrcs, are called ' autogenous,' are printed in zvgapopi.piu.--''' W '^ Roman type ; the italics denote the ' exogenous' W"'--- hiemai spine. parts, uiore properly called 'processes,' which Ideal typical Tcvtcbra. shoot out from the preceding elements. On comparing this form of the primary segment with that figured in Cut 4, p. 5, it will be seen that they differ by altered proportions with some change of position of certain elements ; but every modification resulting in the various forms of the parts of the skeleton figured in PI. 1, has its seat in one or other of the segmental or ' vertebral' elements above defined ; and the same principle I believe that I have established with regard to the internal skeleton in all vertebrate animals. With this preliminary explanation, the nature and relations to the typical vertebra of the parts of the Crocodilian vertebrae, figured in Plates 1 D, 3, will be, it is hoped, readily appi'eciated. In Plate 1 D, in which are figured some of the most perfectly- preserved fossil reptilian vertebrae which have hitherto been discovered, the elements and processes are indicated by the initial letter of their names. Figs. 1 and 2 give a side view and a back view of a cervical vertebra, apparently the fourth, of the CrocodUits Ilasdiif/nia:, from the Eocene deposits at Hordwell ; c is the centrum, n the neural canal formed by the neurapophyses, which have coalesced superiorly with each other, and with the neural spine {ns). Inferiorly they articulate by a suture (which is shown by the wavy line on each side of the process d in fig. 1 ) vdt\\ the centrum ; pi is the pleurapophysis, which articulates by two parts, the lower one called the ' head' to the process from the centrum, the upper one called the ' tubercle' to the process from the neurapophysis ; beyond the union of the head and tubercle, the pleurapophysis projects freely outwards and downwards, but instead of being elongated in that direction, it becomes expanded in the direction of the axis of the body, i. e. forwards and backwards, and so acquires a shape which has given rise to the name ' hatchet bone' or ' hatchet-shaped process,' * applied to this element in the Plesiosaurus. * " To compensate for the weakness that would have attended this great elongation of the neck, the Plesiosaurus had an addition of a series of hatchet-shaped processes on each side of the lower part of the cervical vertehra." (Buckland, Bridgcwatcr Treatise, vol. i, p. 206, and vol. ii, p. 30, 1836.) Cuvier recognised in these lateral bones, " cu forme de liache," the homologues of the " petites cotes cervicales" of the Crocodile. (Ossemens Fossiles, 4to, torn, v, pt. ii, p. 479, 1824.) And Conybeare had CROCODILIA. 85 The purport of this modification is the same in the Crocodilia as that which seems to be more called for in the Plesiosaurus, viz. to augment the strength of the cervical region of the skeleton ; and this is so effectually done by the overlapping of the hatchet- shaped ribs of this region in the Crocodilia, as shown in Plate 1 , that the flexibility of the neck is much restricted, although the joint of the head allows that part to be bent from side to side at nearly right angles with the neck. When, however, the head is held firmly forwards by its powerful muscles, the imbricated vertebrse of the neck transmit with great effect the impulse which the strong and long tail gives to the rest of the body in the act of swimming. In fig. 3 the cervical vertebra is represented minus its pleurapophyses, and it answers accordingly to that portion of the natural segment to which the term ' vertebra' is usually restricted in the dorsal region of the trunk. The exogenous processes shown in this view of the vertebra are, ^j, the ' parapophysis' or inferior transverse process, developed from the centrum ; d, the ' diapophysis' or upper transverse process de- veloped, as in most cases it is, from the neurapophysis ; z, z, are the ' zygapophyses' or ' oblique processes,' which, from their function in articulating together contiguous vertebrae, are also called ' articular processes.' In most of the cervical, and in some of the dorsal, vertebrae of the Crocodile, an exogenous process is developed from the under surface of the centrum, called ' hypapophysis ;' it is indicated by the letters hy in fig. 2. In some species it is double,* and beneath the atlas it becomes ' autogenous' or is developed as a separate element, ca, ex, fig. 8, in which condition the part is found beneath the centrums of two or three of the anterior cervical vertebras in the Ichthyosaurus. f The first and second vertebrae of the neck are peculiarly modified in most air- breathing Vertebrata, and have accordingly received the special names, the one of ' atlas,' the other of ' axis.' In Comparative Anatomy these become arbitrary terms, the properties being soon lost which suggested those names to the human anatomist ; the ' atlas' e. g. has no power of rotation upon the ' axis' in the Crocodile, and it is only in the upright skeleton of man that the large globular head is sustained upon the shoulder- hke processes of the ' atlas.' In the Crocodile, these vertebrae are concealed by the pecvdiarly prolonged angle of the lower jaw in the side view of the skeleton in Plate 1 , and a woodcut of the , ,, , , • , , ' Atlas and Axis vertebrie two vertebrae is therefore subjoined. The pleurapophyses are of the Crocodile. previously extended the same homology to the "particularly prominent wing-like appendages to the transverse processes in many of the long-necked quadrupeds, and the long styloid processes of the cervical vertebra of birds." (See his admirable Memoir of June 1 Ith, 1822, in the Geol. Trans., 2d series, vol. i, p. 384.) * In Crocodilus basifissus, e. g., see the Quarterly Journal of the Geological Society, November 1849, p.381,pl. X, fig. 2. t This interesting discovery was communicated by its author, Sir Phihp de M. Grey Egerton, Bart., to the Geological Society of London, in 18.36, and is published in the fifth volume of the second series of their Transactions, p. 187, pi. 14. N 86 BRITISH FOSSIL REPTILES. retained in both segments, as in all the other vertebrte of tlie trunk. That of the atlas, fig. 8, pi. a, is a simple slender style, articulated by the head only, to the independently developed inferior part of the centrum, or ' hypapopliysis' (ra, ex). The neurapophyses {no) of the atlas retain their primitive distinctness ; each rests in part upon the proper body of the atlas (ca), in part upon the hypapophysis. The neural spine {ns, a) is also here an independent part, and rests upon the upper extremities of the neurapophyses. It is broad and flat, and prepares us for the farther metamorphosis of the corresponding element in the cranial vertebrae. The centrum of the atlas {ca), called the odontoid process of the axis in Human Anatomy, here supports the abnormally-advanced rib of the axis vertebra, which in some Crocodilia is articulated by a bifurcate extremity, like the ribs of the succeeding cervical vertebrae ; but it is not expanded or hatchet-shaped at the free extremity. The proper centrum of the axis vertebra {c,r) is the only one in the cervical series which does not support a rib ; it articulates by suture with its neurapophyses {nx), and is characterised by having its anterior surface flat, and its posterior one convex. With the exception of the two sacral vertebrae, the bodies of which have one articular surface flat and the otlier concave, and of the first caudal vertebra, the body of which has both articular surfaces convex, the bodies of all the vertebrse beyond the axis have the anterior articular surface concave, and the posterior one convex, and articulate with one another by ball-and-socket joints. This type of vertebra, which I have termed ' procoe- lian,'* characterises all the existing genera and species of the family Crocodilia, with all the extinct species of the tertiary periods, and also two extinct species of the Greensand formation in New Jersey. f Here, so far as our present knowledge extends, the type was lost, and other dispositions of the articular surfaces of the centrum occur in the vertebrae of the Crocodilia of the older secondary formations. The only known Crocodihan genus of the periods antecedent to the Chalk and Greensand deposits with vertebrae articulated together by ball-and-socket joints, have the position of the cup and the ball the reverse of that in the modern Crocodiles, and the genus, thus cha- racterised by vertebrae of the ' opisthococlian' type, has accordingly been termed Streptospotidi/hi.s, signifying ' vertebrae reversed.' The aspects of the zygapophyses are, however, more constant ; the anterior ones, PI. 1 D, fig. 3 ~, look obliquely inwards ; the posterior ones, ib. ~', obliquely outwards. In a vertical section, therefore, of a Crocodilian vertebra, such as is figured in PI. 4, fig. 3, the smooth, flattened inner surface of the anterior zygapophysis is turned towards the observer, and the convex outer surface of the posterior zygapophysis. Thus the anterior and posterior extremity of the vei'tebra being determined by observation of the aspect and direction of the zygapophyses, it is at once seen whether the body has the procoelian structure, as in PI. 4, fig. 3, or the opisthococlian structure, as in fig. 4. But the most prevalent type * npos, before ; koiXos, concave. f . Quarterly Journal of the Geological Society, November 1849. CROCODILIA. 87 of vertebra amongst the Crocodilia of the secondary periods was that in which both articular surfaces of the centrum were concave, but in a less degree than in the single concave surface of the vertebrae united by ball and socket. A section of a vertebra of this ' amphicoelian' type, such as existed in the Teleosaurus and Steneoscmrus, is figured in PI. 4, fig. 6. In the Ichtlnjosaurm, the concave surfaces are usually deepened to the extent and in the form shown in fig. 7. Some of the most gigantic of the Crocodilia of the secondary strata had one end of the vertebral centrum flattened, and the other (hinder) end concave ; this ' platycoehan' type we find in the dorsal and caudal vertebrae of the gigantic Cetiosaums (PI. 4, fig. 5). With a few exceptions, all the modern Reptiles of the order Lacertilia have the same procoelian type of vertebrae as the modern Crocodilia, and the same structure prevailed as far back as the period of the Mosasaurus, and in some smaller members of the Lacertilian order in the Cretaceous and Weal den epochs. Resuming the special description of the osteology of the modern Crocodilia, we find the procoelian type of centrum established in the third cervical, which is shorter but broader than the second ; a parapophysis is developed from the side of the centrum, and a diapophysis from the base of the neural arch ; the pleurapophysis is shorter, its fixed extremity is bifid, articulating to the two above-named processes ; its free ex- tremity expands, and its anterior angle is directed forwards to abut against the inner surface of the extremity of the rib of both the axis and atlas, whilst its posterior pro- longation overlaps the rib of the fourth vertebra. The same general characters and imbricated coadaptation of the ribs characterise the succeeding cervical vertebrae to the seventh inclusive, the hypapophysis {/i!/, fig. 2, PL 1 B) progressively though slightly increasing in size. In the eighth cervical the rib becomes elongated and slender ; the anterior angle is almost or quite suppressed, and the posterior one more developed and produced more downwards, so as to form the body of the rib, which terminates, however, in a free point. In the ninth cervical the rib is increased in length, but is still what would be termed a 'false' or ' floating rib' in anthropotomy. In the succeeding vertebra the pleurapophysis articulates with a haemapophysis, and the haemal arch is completed by a haemal spine ; and by this completion of the typical segment we distinguish the commencement of the series of dorsal vertebrae. With regard to the so-called ' perforation of the transverse process,' this equally exists in the present vertebra, as in the cervicals, as may be seen by comparing fig. 6, p. 5, with fig. 2, PI. 1 D; in both, the foramen is the vacuity intercepted between the bifurcate extremity of the rib and the rest of the vertebra with which that rib articulates ; and, on the other hand, the cervical vertebrae equally show surfaces for the articulation of ribs. Cuvier, in including the proximal portions of the ribs with the rest of the vertebra, in his figure of a dorsal vertebra of a Crocodile, * so far follows nature, and produces a parallel to * Ossemens Fossiles, -Ito, torn, v, pt. ii, pi. iv, fig. 4. 88 BRITISH FOSSIL REPTILES. his figure of a cervical vertebra ; but the entire natural vertebra or segment includes the parts delineated in outline in Cut G, p. 5. In that figure is shown the semiossified bar // which is interposed between the pleurapophysisj?^/ and hfemapopliysis // in the Crocodilia and some existing Lizards. The typical characters of the segment due to the completion of both neural and litcmal arches, is continued in some species of Crocodilia to the sixteenth, in some {Crocodilus acutns) to the eighteenth vertebra. In the Crocodilus acutns and the AUiyafor lucius, the hsemapophysis of the eighth dorsal rib (seventeenth segment from the head) joins that of the antecedent vertebra. The pleurapophyses project freely outwards, and become 'floating ribs' in the eighteenth, nineteenth, and twentieth vertebrae, in which they become rapidly shorter, and in the last appear as mere appendages to the end of the long and broad diapophyscs : but the hgemapophyses by no means disappear after the solution of their union with their pleurapophyses ; they are essentially independent elements of the segment, and they are continued, therefore, in pairs along the ventral surface of the abdomen of the Crocodilia, as far as their modified homotypes the pubic bones. They are more or less ossified, and are generally divided into two or three pieces. Another character afi'orded by the haemal arch is the more important in reference to palaeontology, as it affects the centrum and neural arch of the vertebra as well as the pleurapophysis ; and thus aids in the determination of the vertebra. The parapophysis progressively ascends upon the side of the centrum in the two anterior dorsal vertebrae, and disappears in the third, or, passing upon its neurapophysis, blends with the base of the diapophysis. In this segment, therefore, the proximal end of the rib ceases to be bifurcate, but is simply notched, the curtailed head being applied to the end of the thickened anterior part of the transverse process, and the tubercle abutting against its extremity ; in the five following dorsals the head and tubercle of the rib progressively approximate and blend together, or the head disappears in the tenth dorsal, in which the rib is simply attached to the end of the diapophysis. The hypapophysis ceases to be developed after the third or fourth dorsal vertebrae. The zygapophyses become gradually more horizontal, the anterior ones looking more directly upwards, the posterior ones downwards. The ' lumbar vertebrae' are those in which the diapophyses cease to support moveable pleurapophyses, although they are elongated by the coalesced rudiments of such which are distinct in the young Crocodilia. The development and persistent individuality of more or fewer of these rudimental ribs determines the number of the dorsal and lumbar vertebrae respectively, and exemplifies the purely artificial character of the distinction. The number of vertebrae or segments between the skull and the sacrum, in all the Crocodilia I have yet examined, is twenty-four. In the skeleton of a Gavial I have seen thirteen dorsal and two lumbar ; in that of a Crocodilus cafa- phractus twelve dorsal and three lumbar ; in those of a Crocodilus acutus, and Allir/afor lucius, eleven dorsal and four lumbar, and this is the most common number ; but in CROCODILIA. 89 tlic skeleton of tlie Crocodile, I believe of the species called Croc, biporcatus, described by Cuvier,* he gives five as the number of the lumbar vertebree. But these varieties in the development or coalescence of the stunted pleurapophysis are of little essential moment; and only serve to show the artificial character of the 'dorsal' and 'lumbar' vertebrae. The coalescence of the rib with the diapophysis obliterates of course the character of the ' costal articular surfaces ;' which we have seen to be common to both dorsal and cervical vertebrae. The lumbar zygapophyses have their articular surfaces almost horizontal, and the diapophyses, if not longer, have their antero-posterior extent somewhat increased ; they are much depressed, or flattened horizontally. The sacral vertebrae are very distinctly marked by the flatness of the coadapted ends of their centrums ; there are never more than two such vertebrae inthQ Cwcodilia recent or extinct : in the first the anterior surface of the centrum is concave ; in the second it is the posterior surface ; the zygapophyses are not obliterated in either of these sacral vertebrae, so that the aspects of their articular surface — upwards in the anterior pair, downwards in the posterior pair — determines at once the corresponding extremity of a detached sacral vertebra. The thick and strong transverse processes form another characteristic of these vertebrae ; for a long period the suture near their base remains to show how large a proportion is formed by the pleurapophysis. This element articulates more with the centrum than with the diapophysis developed from the neural arch : f it terminates by a rough, truncate, expanded extremity, which almost or quite joins that of the similarly but more expanded rib of the other sacral vertebrae. Against these extremities is applied a supplementary costal piece, serially homologous with the appendage to the proper pleurapophysis in the dorsal vertebrae, but here interposing itself between the pleurapophyses and haemapophyses of both sacral vertebras, not of one only. This intermediate pleurapophysial appendage is called the ' ilium ;' it is short, thick, very broad, and subtriangular, the lower truncated apex forming with the connected extremities of the haemapophysis an articular cavity for the diverging appendage, called the ' hind leg.' The haemapoph)^sis of the anterior sacral vertebra is called ' pubis ;' it is moderately long and slender, but expanded and flattened at its lower extremity, which is directed forwards towards that of its fellow, and joined to it through the intermedium of a broad, cartilaginous, haemal spine, completing the haemal canal. The posterior haemapophysis is broader, subdepressed, and subtriangular, expanding as it approaches its fellow to complete the second haemal arch ; it is termed ' ischium.' The great development of all the elements of these luemal arches, and the peculiar and distinctive forms of those that have thereby acquired, from the earliest dawn of anatomical science, special names, relates phy- * Tom. cit., p. 95. It is to be observed that Cuvier begins to couut the dorsal vertebra when the rib has changed its hatchet-shape for a styloid shape. f Cuvier, who well describes this structure, remarks, "aussi raeritent-elles plutot le nom des cotes que celiii d'apophyses transverses." (Tom. cit., p. 98.) 90 BRITISH FOSSIL REPTILES. siologically to tlie functions of the diverging appendage which is developed into a potent locomotive member. This hmb appertains properly, as the pi-oportion contri- buted by the ischium to the articular socket and the greater breadth of the pleura- pophysis show, to the second sacral vertebra ; to which the ilium chiefly belongs. The first caudal vertebra, which presents a ball for articulating with a cup on the back part of the last sacral, retains, nevertheless, the typical position of the ball on the back part of the centrum ; it is thus biconvex, and the only vertebra of the series which presents that structure. I have had this vertebra in three different species of extinct Eocene Crocodilia. In the Crocodilus toliapicus, PI. 5, fig. 7 ; in the Croc, champso'ides, PL 3v^, fig. 10; and in the Crocodilus Ilastinf/sia;, PL 1 D, fig. 7. The advantage of possessing such definite characters for a particular vertebra is, that the homologous vertebra may be compared in different species, and may yield such distinctive characters as will be hereafter pointed out in those of the three species above cited. The first caudal vertebra, moreover, is distinguished from the rest by ha\'ing no articular surfaces for the hfemapopliyses, which in the succeeding caudals form a haemal arch, like the neurapophyses above, by articulating directly with the centrum. The arch so formed has its base not applied over the middle of a single centrum, but like the neural arch in tlie back of the tortoise and sacrum of the bird, across the interspace between two centrums. The first hsemal arch of the tail belongs, however, to the second caudal vertebra, but it is displaced a little backwards from its typical position. The detached centrum of a caudal vertebra, besides being more slender and com- pressed, is distinguished from those of the before-described vertebrae by the two articular surfaces at the posterior border of their under surface. The zygapophyses become vertical as far as the sixteenth or seventeenth, beyond which the two posterior zygapophyses coalesce in an oblique plane notched in the middle, which is received into a wider notch at the fore pai't of the neural arch of the succeeding vertebra. The sutures between the pleurapophyses and diapophyses are maintained during a long period of the animal's growth, and demonstrate the share which these two elements respectively take in the formation of the transverse process. So constituted, these processes progressively decrease in length to the fifteenth or sixteenth caudal vertebra, and then disappear. The neural spines progressively decrease in every dimension, save length, which is rather increased as far as the twenty-second or twenty-third vertebra, beyond which they begin again to shorten, and finally subside in the tei'minal vertebrae of the tail. The caudal hcemapophyses coalesce at their lower or distal ends, from which a spinous process is prolonged downwards and backwards ; this grows shorter towards the end of the tail, but is compressed and somewhat expanded antero-posteriorly. The hsemal arch so constituted has received the name of ' chevron bone.' A side view of the body of a middle caudal vertebra of the Crocodilus toUapicus is CROCODILIA, 91 given in PI. 3, fig. 8, and an under view of the same in fig. 9, showing the two hyp- apophysial ridges extending from tlie articular facets for the hsemapophyses atone end to the other end of the centrum. The segments of the endo-skelcton composing the skull are more modified than those of the pelvis ; but just as the vertebral pattern is best preserved in the neural arches of the pelvis, which are called collectively ' sacrum,' so, also, is it in the same arches of the skull, which are called collectively ' cranium.' The elements of which these cranial arches are composed preserve, moreover, their primitive or normal individuality more completely than in any of the vertebrre of the trunk, except the atlas, and consecpiently the archetypal character can be more completely demonstrated. In fossil Crocodilia, and many other reptiles, the bones of the head are very liable from this cause to a greater extent of dislocation and separation than happens to the skull of the warm-blooded animal, in which a greater proportion of those primitive bones coalesce with age. It not unfrequently happens that detached bones of the skull of a reptile are found fossil, and the usually much modified form of these vertebral elements renders their determination difficult. In order to diminish this difiiculty, I subjoin some figures of the individual bones from my work on the ' Archetype of the Vertebrate Skeleton,' with such indication of their natural connexions, as is compatible with a clear outline. A profile or side view of all the bones is offered in fig. 13, and as those of the cranium are least familiar to the pateontologist in their detached state, I have added a direct view of them nearly as they are arranged in the formation of the successive neural arches of the skull. Such figures are the more necessary in the present state of anatomy and palaeontology, since the illustrations of the osteology of the crocodile which have hitherto been prefixed to the descriptions of the fossil remains of the Reptilian class, as, e. g., in the great work of Cuvier, include only figures of the bones in question as they are naturally combined together in the entire skull. If, after separating the atlas from the occiput, we proceed to detach the occipital segment of the cranium from the next segment in Pi„. g. advance, we find the detached segment presenting the form of the neural arch, and it is easily and naturally divisible into the four bones figured in Cut 9. The dotted circle crosses the mars-ins at which the bones were joined v together, in order to encompass the hindmost segment of the brain, called ' epencephalon,' whence this neural arch of the occiput is termed ' epencephalic arch.' No. 1 is the base of the arch, and is the 'centrum' or Bonesoftliedisarticulatedepencephalic body of the whole occipital vertebra : it presents, like arch, viewed from behind (Crocodae). those of the trunk, a convexity or ball at its posterior articular surface, but its anterior one, like the hindmost centrum of the sacrum, unites with the next centrum in advance by a flat rough ' sutural' or ' symphysial' surface. Like most of the centrums in the 92 BRITISH FOSSIL REPTILES. neck and beginning of the back, that of the occiput developes a ' hypapophysis,' but this descending process is longer and larger, its base extending over the whole of the under surface of the centrum. It is a character whereby the occipital centrum of a Crocodilian reptile may be distinguished from that of a Lacertian one; for in the latter a pair of diverging hypapophyses project from the under surface, as is shown in most recent lizards and in the great extinct Mosasaurus* The upper and lateral parts of no. i present rough sutural surfaces, like those in the centrums of the trunk, for articulating with the ' neurapophyses,' nos 2, 2, which developc short, thick, obtuse, transverse processes (4, 4). The modified or specialized character of the elements of the cranial vertebne has gained for them special names. The centrum (1) is called the ' basioccipital ;' the neurapophyses (2,2) are the ' ex- occipitals ;' the neural spine (3) is the ' superoccipital.' The transverse processes (4, 4), which may combine both diapophyses and parapophyses, but which, from the modifications of the transverse processes of the atlas, and the autogenous character of the parapophyses in some fishes, and of the processes in question in the Chelonian Reptiles, I believe to be best entitled to be regarded as the parapophyses, are called the ' paroccipitals ;' they are never detached bones in the Crocodilia, as they are in the Chelonia and in most fishes. The exoccipitals perform the usual functions of neurapophyses, and, like those of the atlas, meet above the neural canal ; they are perforated to give exit to the vagal and hypoglossal nerves, and protect the sides of the medulla oblongata and cerebellum — the two divisions of the epencephalon. The superoccipital (3) is broad and flat, like the similarly detached neural spine of the atlas ; it advances a little forwards, beyond its sustaining neurapophyses, to protect the upper surface of the cerebellum : it is traversed by tympanic air-cells, and assists with the exoccipitals (2, 2) in the formation of the chamber for the internal ear. The chief modification of the occipital segment of the skull, as compared with that of the osseous fish, or with the typical vertebra, is the absence of an attached htemal arch. We shall afterwards see that this arch is present in the Crocodile, although displaced ; a profile of it is given, as restored to its typical position, in the side view of the bones of the skull, fig. 13. Proceeding with the neural arches of the Crocodile's skull, if we dislocate the segment in advance of the occiput, we bring away in connexion with the long base-bone, 5 and 9, fig. 13, the bones which, in the same figure, are tied together by the double lines, N 11, N in, and by the curved arrows, H 11 and H in. In fact, the centrums of two vertebrae have here coalesced, as we find to happen in the neck of the Siluroid fishes, and in the sacrum of birds and mammals. The two connate cranial centrums must be artificially divided, in order to obtain the segments distinct to which they belong. Fig. 10 gives a back view of the disarticulated bones of the neural * See Quarterly Journal of the Geological Society, Nov. 1, )S49, p. 382, pi. x, figs. 5, 6. CROCODILIA. 93 arch of the ' parietal vertebra,' as the segment is termed which is in advance of the occipital one. The hinder portion (5) of the great base-bone, which is the centrum of the parietal vertebra, is called 'basisphenoid.' Fig. 10. It supports that part of the ' mesencephalon,' which is formed by the lobe of the third ventricle, and its upper surface is excavated for the pituitary prolongation of that cavity. The basisphenoid developes from its under surface a ' hypapophysis,' which is suturally united with the fore part of that of the basioccipital, but extends further down, and is similarly united in front to the ' pterygoids' (24). These rough sutural surfaces of the long descending process of the basisphenoid are very Disarticulated mesencephalic arch, viewed characteristic of that centrum, when detached in fto"i bcliind (Crocodile). a fossil state. The neurapophyses of the parietal vertebra (G, 6) are called the ' ali- sphenoids ;'* they protect the sides of the mesencephalon, and are notched at their anterior margin, for a conjugational foramen transmitting the trigeminal nerve. As accessory functions they contribute, like the corresponding bones in fishes, to the formation of the ear-chamber. They have, however, a little retrograded in position (see fig. 14, 6), resting below, in part upon the occipital centrum, and supporting more of the spine of that segment (3) than of their own (7)- The spine of the parietal vertebra (fig. 10, 7) is a permanently distinct, single, depressed bone, like that of the occipital vertebra ; it is called the ' parietal,' and completes the neural arch, as its crown or key-bone ; it is partially excavated by the tympanic air-cells. The bones 8, 8 wedged between 6 and 7, manifest more of their parapophysial character than their homotypes (4, 4) do in the occipital segment, since they support modified ribs, are developed from independent centres, and preserve their individuality. They form no part of the inner walls of the cranium, but send outwards and backwards a strong transverse process for muscular attachment. They afford a ligamentous attachment to the haemal arch (fig. 13, H 11) of their own segment, and articulate largely with the pleurapophysis (28) of the antecedent haemal arch (H iii), whose more backward dis- placement, in comparison with its position in the fish's skull, is well illustrated in the metamorphosis of the toad and frog. On removing the neural arch of the parietal vertebra, after the section of its confluent centrum, the elements of the corresponding arch of the frontal vertebra, slightly disarticulated, present the arrangement shown in fig. 11. The compressed produced centrum (9) shown in natural connexion with the parietal centrum 5 in fig. 13, * This bone is the ' rocher' or petrous portion of the temporal bone, according to Cuvier, in the Reptiles (Ossemens Fossiles, v, pt. ii, 1824) ; but is the 'aile temporalc du spheuoide' in fishes (Histoire Naturellc des Poissons, torn, i, 1828), birds, and mammals. O 94 BRITISH FOSSIL REPTILES. Disarticulated proaenceplialic arch, viewed from behind (Crocodile). and with the bone lo in fig. 14, has its form modified like that of the vertebral centrums at the opposite extreme of the body in many birds ; it is called the ' presphenoid.' Eig. 11. Theneurapophyses 10, lO, articulate with the upper part of 9 ; they are expanded and smoothly excavated on their inner surface to support the sides of the large prosencephalon ; they dismiss the great optic nerves by the notch marked op in fig. 14, and the motor nerves of the eyeball by the notch s. They show the same tendency to a retrograde change of position, as the neighbouring neurapophyses {(t) ; for though they support a greater proportion of their proper spine (ii), they also support part of the parietal spine (7), and rest, in part, below upon the parietal centrum (.')) : the neurapophyses (10, lO) are called ' orbitosphenoids.'* The neural spine (11) of the frontal vertebra retains its normal character as a single symmetrical bone, like the parietal spine which it partly overlaps ; it also completes the neural arch of its own segment, but is remarkably extended longitudinally forwards, as is shown in figs. 13 and 14, 11, where it is much thickened, and assists in forming the ca^^ties for the eyeballs {or, fig. 14) : it is called the (frontal) bone. In contemplating in the skull itself, or in such side views as are given in figs. 13 and 14, the relative position of the frontal (11), to the parietal (7), and of this to the superoccipital (3), which is overlapped by the parietal, just as itself overlaps the flattened spine of the atlas, we gain a conviction which cannot be shaken by any difi"erence in their mode of ossification, by their median bipartition, or by their extreme expansion in other animals, that the above-named single, median, imbricated bones, each completing its neural arch, and permanently distinct from the piers of such arch, must repeat the same element in those successive arches, in other words, must be ' homotypes,' or serially homologous.! In like manner the serial homology of those piers, called ' neur- apophyses,' viz. the laminse of the atlas (fig. 8 na), the exoccipitals (figs. 13 and 14, 2), the alisphenoids (e), and the orbitosphenoids (10), is equally unmistakable. Nor can we shut out of view the same serial relationship of the paroccipitals (4), as coalesced parapophyses of the occipital vertebra, with the mastoids (s), and the postfrontals (12), as permanently detached parapophyses of their respective vertebrse. All stand out from the sides of the cranium, as transverse processes for muscular attachment, all are alike autogenous in the Chelonians, and all of them, in fishes, ofifer articular surfaces * According to Cuvier, this bone is the ' aile temporale Ju sphenoide et une grande partie de I'aile orbitaire' in Crocodiles. (Ossemens Fossiles, torn, v, pt. ii.) t See my work 'Ou the Archetype of the Vertebrate Skeleton,' pp. 5-8, 8vo, Van Voorst, for the expla- nation of these terms. CHOCODILIA. 95 Fig. 12. for the ribs or haemal arches of their respective vertebrae ; and these characters are retained in the postfrontals as well as in the mastoids of the Crocodiles. The frontal parapophysis ( 12, fig. U) is wedged between the back part of the spine (ll) and the neurapophysis (lo) ; its outwardly projecting process extends also back- wards and joins that of the succeeding parapophysis (s) ; but, notwithstanding the retrogradation of the inferior arch (fig. 13, H iii), it still articulates with part of its own pleurapophysial element (28), which forms the proximal element of that arch. There finally remain in the cranium* of the Crocodile, after the successive detach- ment of the foregoing arches, the bones intersected by the double line N iv, in fig. 13, which, as in fig. 14, are numbered 13, U, and 15, and of which a foreshortened back view is represented in Cut 12 ; but, notwithstanding the extreme degree of modification to which their extreme position subjects them, we can still trace in their arrangement a correspondence with the vertebrate type. A long and slender symmetrical grooved bone (i3, between 24, 24), like the ossified inferior half of the capsule of the notochord, is con- tinued forwards from the inferior part of the cen- trum (y) of the frontal vertebra, and stands in the relation of a centrum to the vertical plates of bone (14), fig. 12, and fig. 14, which expand as they rise into a broad, thick, triangular plate, with an exposed hori- zontal superior surface. These bones, which are called ' prefrontals,' stand in the relation of ' neurapophyses' to the rhinencephalic prolongations of the brain, com- monly but erroneously called ' olfactory nerves ;' and they form the piers or haunches of a neural arch, which is completed above by a pair of symmetrical bones (15) called ' nasals,' which I regard as a divided or bifid neural spme. Disarticulated rhinencephalic arch, with The centrum of this arch is established by ossifi- the anchylosed pterygoids (24) in dotted cation in the expanded anterior prolongation of the "'^^^'^^ (Crocodne). fibrous capsule of the notochord, beyond the termination of its gelatinous axis. The * The part called cranium in human anatomy is a quite artificial division of the skull ; it includes the neurapophyses of the nasal vertebrae, coalesced with the capsules of the sense of smell, and excludes the centrum and neural arch of the same natural segment ; it also includes one portion of the diverging appendage (27) of the maxillary arch, because it enters largely into the formation of the capacious cranial cavity of man, and another portion of the diverging appendage of the same arch (24), because it happens to coalesce with the basisphenoid. The capsule of the organ of hearing is included together with part of that of the olfactory organ, whilst the capsule of the organ of sight, and part of that of the organ of smell are excluded. None of these sense-capsules properly form any part of the cranium, but they are lodged in interspaces of its constituent arches. The cranial portion of the skuU, as a natural division of that part of the endoskeleton, ought to consist exclusively of the neural arches and centrums of the cranial vertebrae. 96 BRITISH FOSSIL REPTILES. median portion above specified retains most of tlie formal characters of the centrum, but there is a pair of long, slender, symmetrical ossicles, which, from the seat of their original development, and their relative position to the neural arch, must be regarded as also parts of its centrum. And this ossification of the element in question from different centres will be no new or strange character to those who recollect that the vertebral body in man and mammalia is developed from three centres. The term 'vomer' is applied to the pair of bones 13, in fig. 12, because their special homology with the single median bone, so called in fishes and mammals, is indisputable; but a portion of the same element of the skull retains its single symmetrical character in the Crocodile, and is connate with the enormous pterygoids (24), between which it is wedged. In some Alligators {All. niger) the divided anterior vomer extends far forwards, expands anteriorly, and appears upon the bony palate. Almost all the other bones of the head of the Crocodile are adjusted so as to constitute four inverted arches, respectively completed or closed below at the points marked H iv, H iii, H ii, and H i, in fig. 13. These are the haemal arches of the four segments or vertebrae, of which the neural arches have been just described. But they have been the seat of much greater modifications, by which they are made sub- servient to a variety of functions unknown in the haemal arches of the rest of the body. Thus the two anterior haemal arches of the head perform the office of seizing and bruising the food ; are armed for that purpose with teeth : and, whilst one arch is firmly fixed, the other works upon it like the hammer upon the anvil. The elements of the fixed arch (H iv), called ' maxillary arch,' have accordingly undergone the greatest amount of morphological change in order to adapt that arch to its share in mastication, as well as for forming part of the passage for the respiratory medium, which is perpetually traversing this haemal canal in its way to purify the blood. Almost the whole of the upper surface of the maxillary arch is firmly united to contiguous parts of the skuU by rough or sutural surfaces, and its strength is increased by bony appendages, which diverge from it to abut against other parts of the skull. Comparative anatomy teaches that, of the numerous places of attachment, the one which connects the maxillary arch by its element (20) with the centrum (13) and the descending plates of the neurapophyses (14) of the nasal segment, is the normal or the most constant point of its suspension, the bone (20) being the pleurapophysial element of the maxillary arch : it is called the 'palatine,' because the under surface, shown in PI. A, 2, and PI. 1 B, at 20, forms a portion of the bony roof of the mouth called the ' palate.' It is articulated at its fore part with the bone (21) in the same plates, which bone is the haemapophysial element of the maxillary arch. It is called the ' maxillary,' and is greatly developed both in length and breadth ; it is connected not only with 20 behind, and 22 in front, which are pai'ts of the same arch (see fig. 13), and with the diverging appendages of the arch, viz. (26) the malar bone, and (24) the pterygoid, but also with the nasals (15) and the lachrymal (ic), as well as with its fellow of the CROCODILIA. 97 opposite side of the arch. The smooth expanded horizontal plate which efifects the latter junction, shown in PI. 1 B, and PI. A % at 21, is called the palatal plate of the maxillary ; the thickened external border, where this plate meets the external rough surface of the bone, and which is perforated for the lodgement of the teeth, is the ' alveolar border' or ' process' of the maxillary. The haemal spine or key-bone of the arch (22) is bifid, and the arch is completed by the symphysial junction of the two symmetrical halves at H iv, fig. 13 ; these halves are called ' premaxillary bones ;' Ym. 13. Disarticulated bones of tlie Skull of an Alligator, N i to iv tlie neui-al arches ; H I to iv the hajmal arches and appendages. these bones, like the maxillaries, have a rough facial plate, PI. 1 A, 22 and a smooth palatal plate PI. 1 B, 22, with the connecting alveolar border. The median symphysis is perforated vertically through both plates ; the outer or upper hole being the external nostril, the under or palatal one being the prepalatal or naso-palatal aperture ; this is completely inclosed by the premaxillary bone, as shown in PI. 1 B, fig. 2, 22, and PI. 1 C, 22, np ; whilst, in all known existing Crocodiles and Alligators, the tips of tlic nasal bones, as at 15, fig. 1, PI- A 2, enter into the back part of the circumference of the nasal aperture. In the Gavials, as may be seen in PI. 1, fig. 1 a, the nasal aperture is wholly surrounded by the premaxillaries, i ; and one of the fossil Eocene Crocodiles, 98 BRITISH FOSSIL REPTILES. presently to be described, PI. 1 A, fig. 1, differs from all the modern species, in the exclusion of the nasal bones (i.i) from the nasal aperture. Both the palatine (fig. 13, 20) and the maxillary (ib. 21) send outwards and back- wards, parts or processes which diverge from the line of the haemal arch of which they are the chief elements ; and these parts give attachment to distinct bones which form the ' diverging appendages' of the arch, and serve to attach it, as do the diverging appendages of the thoracic haemal arches in the bird, to the succeeding arch. The appendage (24) called ' pterygoid' effects a more extensive attachment, and is peculiarly developed in the CrocodiUa. As it extends backwards it expands, unites with its fellow, below the nasal canal, and encompassing that canal, coalesces above it with the vomer, and is firmly attached by suture to the presphenoid and basisphenoid : it surrounds the hinder or palatal nostril, and, extending outwards, as shown in PI. 1 A, fig. 3 (24), it gives attachment to a second bone (25), called ' ectopter}'goid,' which is firmly connected with the maxillary (25), the malar (26), and the post-frontal (12). The second diverging ray is of great strength ; it extends from the maxillary (21) (' haema- pophysis' of the maxillary arch) to the tympanic (28) ('pleurapophyses' of the mandibular arch), and is divided into two pieces, the malar (26), and the squamosal (27). Such are the chief Crocodilian modifications of the haemal arch and appendages of the anterior or nasal vertebra of the skull. The haemal arch of the frontal vertebra is somewhat less metamorphosed, and has no diverging appendage. It is slightly displaced backwards, and is articulated by only a small proportion of its pleurapophysis (28), to the parapophysis (12) of its own segpient ; the major part of that short and strong rib articulating with the para- pophysis (8) of the succeeding segment. The bone (28) called ' tympanic,' because it serves to support the ' drum of the ear,' in air-breathing vertebrates, is short, strong, and imraoveably wedged, in the CrocodiUa, between the paroccipital (4), mastoid (s), post-frontal (12), and squamosal (27); and the conditions of this fixation of the pleura- pophysis are exemplified in the great development of the haemapophysis (mandible), which is here unusually long, supports numerous teeth, and requires, therefore, a firm point of suspension, in the violent actions to which the jaws are put in retaining and overcoming the struggles of a powerful living prey. The moveable articulation between the pleurapophysis (28) and the rest of the haemal arch is analogous to that which we find between the thoracic pleurapophysis and haemapophysis in the Ostrich and many other birds. But the haemapophysis of the mandibular arch in the Crocodiles is subdivided into several pieces, in order to combine the greatest elasticity and strength with a not excessive weight of bone. The different pieces of this purposely sub- divided element have received definite names. That numbered 29, which offers the articular concavity to the convex condyle of the tympanic (28), is called the ' articular' piece ; that beneath it (30), which dcvelopes the angle of the jaw, when this projects, is the ' angular' piece ; the piece above (29') is the ' surangular ;' the thin, broad, flat CROCODILIA. 99 piece (3i)j applied, like a splint, to the inner side of the other parts of the mandible, is the 'splenial;' the small accessory ossicle (31') is the ' coronoid,' because it developes the process so called, in lizards ; the anterior piece (32), which supports the teeth, is called the ' dentary.' This latter is the homotype of the preraaxillary, or it represents that bone in the mandibular arch, of which it may be regarded as the haemal spine ; the other pieces are subdivisions of the hBemapophysial element. The purport of this subdivision of the lower jaw-bone has been well explained by Conybeare* and Buckland,t by the analogy of its structure to that adopted in binding together several parallel plates of elastic wood or steel to make a crossbow, and also in setting together thin plates of steel in the springs of carriages. Dr. Buckland adds, "those who have witnessed the shock given to the head of a Crocodile by the act of snappino- together its thin long jaws, must have seen how liable to fracture the lower jaw would be, were it composed of one bone only on each side." The same reasoning applies to the composite structure of the long tympanic pedicle in fishes. In each case the spHcing and bracing together of thin flat bones of unequal length and of varyino- thickness, affords compensation for the weakness and risk of fracture that would other- wise have attended the elongation of the parts. In the abdomen of the Crocodile the analogous subdivision of the hsemapophyses, there called abdominal ribs, allows of a slight change of their length, in the expansion and contraction of the walls of that cavity ; and since amphibious reptiles, when on land, rest the whole weight of the abdomen directly upon the ground, the necessity of the modification for diminished liability to fracture further appears. These analogies are important, as demonstratino- that the general homology of the elements of a natural segment of the skeleton is not affected or obscured by their subdivision for a special end. Now this purposive modification of the hsemapophyscs of the frontal vertebra is but a repetition of that which affects the same elements in the abdominal vertebrae. Passing next to the haemal arch of the parietal vertebra (fig. 13, H iir), we are first struck by its small relative size ; its restricted functions have not required it to ^row in proportion with the other arches, and it consequently retains much of its embryonic dimensions. It consists of a ligamentous ' stylohyal' — its pleurapophysis, retaining the same primitive histological condition which obstructs the ordinary recognition of the same elements of the lumbar haemal arches. A cartilaginous ' epihyal' (39) intervenes between this and the ossified ' haemapophysis' (40), which bears the special name of ceratohyal. The haemal spine (41) retains its cartilaginous state, like its horaotypes in the abdomen : there they get the special name of ' abdominal sternum,' here of ' basi- hyal.' The basihyal has, however, coalesced with the thyrohyals, to form a broad cartilaginous plate, the anterior border rising like a valve to close the fauces, and the posterior angles extending beyond and sustaining the thyroid and other parts of the * Geol. Trans., 1821, p. 565. t Bridgewater Treatise, 1836, vol. i, p. 176. 100 BRITISH FOSSIL REPTILES. larynx. The long bony ' ccratohyal' (fig. 13, 40), and the commonly cartilaginous 'cpihyal' (ib. 39), are suspended by the hgamentous ' stylohyal' to the paroccipital process ; the whole arch having, like the mandibular one, retrograded from the con- nexion it presents in fishes. This retrogradation is still more considerable in the succeeding hsemal arch. In comparing the occipital segment of the crocodile's skeleton with that of the fish, the chief modification that distinguishes that segment in the crocodile is the apparent absence of its hsemal arch. We recognise, however, the special homologues of the constituents of that arch of the fishes' skeleton in the bones 51 and 52 of the crocodile's skeleton (fig. 13) ; but the upper or suprascapular piece (50) retains, in connexion with the loss of its proximal or cranial articvilations, its cartilaginous state : the scapula (51) is ossified, as is likewise the coracoid (52), the lower end of which is separated from its fellow by the interposition of a median, symmetrical, partially ossified piece called ' epistefnum' (Hi). The power of recognising the special homologies of 50, 51, and 52 in the crocodile, with the similarly numbered constituents of the same arch in fishes*, though masked, not only by modifications of form and proportion, but even of very substance, as in the case of 50, depends upon the circumstance of these bones constituting the same essential element of the archetypal skeleton; for although in the present instance there is superadded to the adaptive modifications above cited, the rarer one of altered connexions, Cuvier does not hesitate to give the same names, ' suprascapulaire ' to 50 and 'scapulaire' to 51, in both fish and crocodile: but he did not perceive or admit that the narrower relations of special homology were a result of, and necessarily included in, the wider law of general homology. According to the latter, we discern in 50 and 51 a teleologically compound ' pleurapophysis,' in 52 a ' hsemapophysis,' and in hs the ' haemal spine,' completing the haemal arch. The general relations of the scapulo-coracoid arch to a haemal or costal one was early recognised by Oken. This philosopher, having observed the free cervical ribs in a specimen of the Lacerfa apoda, Pallas {Fseudojjus), deemed them representatives of the scapula, and this bone to be, in other animals, the coalesced homologues of the cervical pleurapophyses.f In no animal are the conditions for testing this question so favor- able and obvious as in the crocodiles and ga vials (PI. 1) ; not only do cervical ribs coexist with the scapulo-coracoid arch, but they are of unusual length, and are developed from the atlas as well as from each succeeding cervical vertebra : we can also trace them beyond the thorax to the sacrum, and throughout a great part of the caudal region, as the sutures of the apparently long transverse processes of the * See fig. 5, p. 18, and pi. ii, fig. 2, in ' The Arclietype and Homologies of the Vertebrate Skeleton.' t " Auch die Scapula nicht ein Kuoehen, soudern wenigstens eine aus fiinf Halsrippen zusaminengeflossene Platte iii"— Programmiiher die Bedeutuny der Schiidelhwchen, Aio, 180", p. 16. He reproduces the same idea of the general homology of the scapula in the ' Lehrbuch der Natiir-philosophie,^ 1843, p. 331, ^2381. Cams also regards the scapulo-coracoid arch as the reunion of several (at least three) proto- vertebral arches of the trunk-segments. {Urtheilen des Knochen wid Schalen r/enistes, fol., 1828.) CROCODILIA. 101 coccygeal vertebrae demonstrate in the young animal ; the lumbar pleurapophyses being manifested at the same period as cartilaginous appendages to the ends of the long diapophyses. The scapulo-coracoid arch, both elements (51, 52) of which retain the form of strong and thick vertebral and sternal ribs in the crocodile, is applied in the skeleton of that animal over the anterior thoracic htemal arches. Viewed as a more robust haemal arch, it is obviously out of place in reference to the rest of its vertebral segment. If we seek to determine that segment by the mode in which we restore to their centrums the less displaced neural arches of the antecedent vertebrae of the cranium or in the sacrum of the bird,* we proceed to examine the vertebras before and behind the dis- placed ai'ch, with the view to discover the one which needs it, in order to be made typically complete. Finding no centrum and neural arch without its pleurapophyses from the scapula to the pelvis, we give up our search in that direction ; and in the opposite direction we find no vertebra without its ribs until we reach the occiput : there we have centrum and neural arch, with coalesced parapophyses — the elements answering to those included in the arch N i, fig. 13 — but without the arch H i; which arch can only be supplied, without destroying the typical completeness of antecedent cranial segments, by a restoration of the bones 50 — 52, to the place which they naturally occupy in the skeleton of the fish. And since anatomists are generally agreed to regard the bones 50 — 52 in the crocodile (fig. 13) as specially homologous with those so numbered in the fish,t we must conclude that they are likewise homo- logous in a higher sense ; that in the fish, the scapulo-coracoid arch is in its natural or typical position, whereas in the crocodile it has been displaced for a special purpose. Thus, agreeably with a general principle, we perceive that, as the lower vertebrate animal illustrates the closer adhesion to the archetype by the natural articulation of the scapulo-coracoid arch to the occiput, so the higher vertebrate manifests the superior influence of the antagonising power of adaptive modification by the removal of that arch from its proper segment. The anthropotomist, by his mode of counting and defining the dorsal vertebrae and ribs, admits, unconsciously perhaps, the important principle in general homology which is here exemplified, and which, pursued to its legitimate consequences and further applied, demonstrates that the scapula is the modified rib of that centrum and neural arch which he calls the ' occipital bone,' and that the change of place which chiefly masks that relation (for a very elementary acquaintance with comparative anatomy shows how little mere form and proportion afi"ect the homological characters of bones) differs only in extent and not in kind from the modification which makes a minor amount of comparative observation requisite, in order to determine the relation of the shifted dorsal rib to its proper centrum in the human skeleton. * See 'On the Archetype and Homologies of the Vertebrate Skeleton,' p. 11", p. 159. t Op. cit., fig. 5, p. 17. P 102 BRITISH FOSSIL REPTILES. With reference, therefore, to the occipital vertebra of the crocodile, if the com- paratively well-developed and permanently distinct ribs of all the cen'ical vertebrae prove the scapular arch to belong to none of those segments, and, if that hjemal arch l^e required to complete the occipital segment, which it actually does complete in fishes, then the same conclusion must apply to the same arch in other animals, and we must regard the occipital vertebra of the tortoise as completed below by its scapulo-coracoid arch and not, as Bojanus supposed, by its hyoidean arch.* Having thus endeavoured to show what the scapular arch of the crocodile is, I proceed to point out the characteristic form of its chief elements. The upper and principal part of the scapula (.51, fig. 13) is flattened, and gradually becomes narrower to the part called its neck, which is rounded, bent inwards, and then suddenly expanded to form a rough articular surface for the coracoid, and a portion of a smoother surface for the shoulder-joint. The contiguous end of the coracoid (52) presents a similar form, having not only the rough sui'face for its junction with the scapula, but contributing, also, one half of the cavity for the head of the humerus. It is perforated near the interspace between these two surfaces. As it recedes from them, it contracts, then expands and becomes flattened, terminating in a somewhat broader margin than the base of the scapula, which margin is morticed into a groove at the anterior border of the broad rhomlwidal cartilage continued beyond the ossified part of the manubrium, which forms the key-bone of the scapular arch. The anterior locomotive extremity is the diverging appendage of the arch, under one of its numerous modes and grades of development.f The proximal element of this appendage or that nearest the arch, is called the ' humerus' (53, fig. 13) : its head is subcompressed and convex; its shaft bent in two directions, with a deltoid crest developed from its upper and fore part ; its distal end is transversely extended, and divided anteriorly into two condyles. The shaft of this bone has a medullary cavity, but relatively smaller than in the mammalian humerus. The second segment of the limb consists of two bones : the larger one (54) is called the ' ulna :' it articulates with the outer condyle of the humerus by an oval facet, the * Anatome Testudinis Europpea, fol., 1S19, p. 44. GeofFroy St. Hilaii-e selected the opercular audsub- opercular bones to form the inverted arch of his seventh (occipital) cranial vertebra, and took no account of the instructive natural connexions and relative position of the hyoidean and scapular arches in fishes. With regard to the scapular arch, he alludes to its articulation with the skull in the lowest of the vertebrate classes as an ' amalgame inattendue' {Anatomie Philosophique, p. 481) : and elsewhere describes it as a " disposition veritablement trfes singuliere, et que le manque absolu du cou et une combinaison des pieces du sternum avec celles de la tete pouvoicut seules rendre possible." — Annalesdu Museum, i,\, p. 3()1. A due appreciation of the law of vegetative uniformity or repetition, and of the ratio of its prevalence and power to the grade of organization of the species, was, perhaps, essential in order to discern the true signification of the connexion of the scapular arch in fishes. f See my Discourse ' On the Nature of Limbs,' 8vo, Van Voorst, 1849, pp. 64-/0. CROCODILIA. 103 thick convex border of which swells a Httie out behind, and forms a kind of rudimental ' olecranon ;' the shaft of the ulna is compressed transversely, and curves slightly out- wards ; the distal end is much less than the proximal one, and is most produced at the radial side. The radius (55) has an oval head ; its shaft is cylindrical; its distal end oblong and subcompressed. The small bones (sG) which intervene between these and the row of five longer bones, are called ' carpals :' they are four in number in the Crocodilia. One seems to be a continuation of the radius, another of the ulna ; these two are the principal carpals ; they are compressed in the middle and expanded at their two extremities ; that on the radial side of the wrist is the largest. A third small ossicle projects slightly backwards from the proximal end of the ulnar metacarpal : it answers to the bone called ' pisiforme' in the human wrist. The fourth ossicle is interposed between the ulnar carpal and the metacarpals of the three ulnar digits. These five terminal jointed rays of the appendage are counted from the radial to the ulnar side, and have received special names : the first is called ' poUex,' the second ' index,' the third ' medius,' the fourth ' annularis,' and the fifth ' minimus.' The first joint of each digit is called ' metacarpal ;' the others are termed ' phalanx.' In the Crocodilia the poUex has two phalanges, the index three, the medius four, the annularis four, and the minimus three. The terminal phalanges, which are modified to support claws, are called ' ungual' phalanges. As the above-described bones of the scapular extremity are developments of the appendage of the scapular arch, which is the haemal arch of the occipital vertebra, it follows, that, like the branchiostegal rays and opercular bones in fishes, they are essentially bones of the head. But the enumeration of the bones of the crocodile's skull is not completed by these: there is a bone anterior to the orbit, marked 73 in fig. 13, and in PI. 1 A and J2 ; it is perforated at its orbital border by the duct of the lachrymal gland, whence it is termed the 'lachrymal bone,' and its facial part extends forwards between the bones marked 14, 15, 21, and 26. In many Crocodilia there is a bone at the upper border of the orbit, which extends into the substance of the upper eyelid ; it is called ' superorbital.' In the Crocodllm palpehrosus there are two of these ossicles. Both the lachrymal and superorbital bones answer to a series of bones found com- monly in fishes, and called ' suborbitals' and ' superorbitals.' The lachrymal is the most anterior of the suborbital series, and is the largest in fishes ; it is also the most constant in the vertebrate series, and is grooved or perforated by a mucous duct. These ossicles appertain to the dermal or muco-dermal system or ' exoskeleton ;' not to the vertebral system or ' endoskeleton.' The little slender bone, marked Hi' in fig. 13, has one of its extremities in the form of a long, narrow, elliptic plate, which is applied to the ' fenestra ovalis' of the internal 104 BRITISH FOSSIL REPTILES. Fig. 14. Vertical longitudinal section of the cranium of a Crocodile {Crocodilus acutus). ear ; from this plate extends a long and slender bony stem, which grows somewhat cartilaginous, expands and bends down, as it approaches the tympanum or ear-drum, to which it is attached. The cartilaginous capsule of the labyrinth or internal ear is partially ossified by sinuous plates of bone connate with the neurapophyses (2 and 6), between which that organ is lodged ; I apply the term ' petrosal' to the principal and most independent of those ossifications of the ear-capsule, to that, e. g., which retains some mobility after it has con- tracted a partial anchylosis to the exoccipital (2), and which appears upon the inner surface of the cranial walls at the part marked 16 in the subjoined Cut 14, between 2 and 6. It is the only independent bone on that surface of the cranium which, in my opinion, answers to the ' petrous portion of the temporal' in human anatomy, and to which the term ' roclier' can be properly applied, in the language of the French comparative anatomists. Cuvier, however, restricts that name to the 'ahsphenoid' (6, figs. 13, 14) in the Crocodiles. The ossicles, (16 and 16'), together with the partial ossifications in the sclerotic capsule of the organ of sight, (17, fig. 13) — always more distinct in Chelonia than in Crocodilia — belong to that category of visceral bones to which the term ' splanchno- skeleton' has been given ; they also are foreign to the true vertebrate system of the skeleton. Thus the classification of the bones of the head of the Crocodiles, as of all other vertebrate animals, is primarily into those of The Endo-skeleton, The Splanchno-skeleton, and The EXO-SKELETON. The bones of the endo-skeleton of the head form naturally four segments, called Occipital vertebra, N i, H i ; Parietal vertebra. Nil, H 11 ; Frontal vertebra, N iii, H iii ; Nasal vertebra, N iv, H iv. These segments are subdivided into the neural arches, called Epencephahc arch (1 basioccipital, 2 exoccipital, 3 superoccipital, 4 connate paroccipital) ; Mesencephalic arch (5 basisphenoid, 6 alisphenoid, 7 parietal, 8 mastoid) ; Fig. 13. CROCODILIA. 10.5 Prosencephalic arch (9 presphenoid, 10 orbitosphenoid, 11 frontal, 12 post- frontal) ; Rhinencephalic arch (13 vomer, 14 prefrontal, 15 nasal) : and into the heemal arches and their appendages, called Maxillary arch (20 palatine, 21 maxillary, 22 premaxillary) and appendages (24 pterygoid, 24' ectopterygoid, 26 malar, 27 squamosal) ; Mandibular arch (28 tympanic, 29—32 mandible) ; Hyoidean arch (39 epihyal, 40 ceratohyal, 41 basihyal) ; Scapular arch (50 suprascapula, 51 scapula, 52 coracoid) and appendages (53—58 bones of fore-limb). The bones of the splanchno-skeleton, are The petrosal (16) and otosteals (le') ; The sclerotals (17) which in most retain their primitive histological condition as fibrous membrane. The turbinals (18 and 19) and teeth. The bones of the exo-skeleton, are The lacrymals (73). The superorbitals (present in Alligator sclerqps). There remains to complete this preliminary sketch of the osteology of the Crocodile a brief notice of the bones composing the diverging appendage of the pelvic arch : these being a repetition of the same element as the appendage of the scapular arch modified and developed for a similar office, manifest a very close resemblance to it. The first bone, called the ' femur,' is longer than the humerus, and, like it, presents an enlargement of both extremities, with a double curvature of the intervening shaft, but the directions are the reverse of those of the humerus, as may be seen in PI. 1, where the upper or proximal half of the femur is concave, and the distal half convex, anteriorly. The head of the femur is compressed from side to side, not from before backwards as in the humerus ; a pyramidal protuberance from the inner surface of its upper fourth represents a ' trochanter ;' the distal end is expanded transversely, and divided at its back part into two condyles. The next segment of the hind-limb or ' leg,' includes, like the corresponding segment of the fore-limb called ' fore-arm,' two bones. The largest of these is the ' tibia,' and answers to the radius. It presents a large, triangular head to the femur ; it terminates below by an oblique crescent with a convex surface. The ' fibula' is much compressed above ; its shaft is slender and cylindrical, its lower end is enlarged and triangular. All these long bones have a narrow medullary cavity. The group of small bones which succeed those of the leg, are the tarsals ; they are four in number, and have each a special name. The ' astragalus' articulates with the tibia, and supports the first and part of the second toe. It is figured in Cuvier's 106 BRITISH FOSSIL REPTILES. 'Osscmen's Fossiles,' torn, v, pt. ii, pi. iv, figs. 19 J, B, C, D. The 'calcaneum' inter- venes between the fibula and the ossicle supporting the two outer toes ; it has a short but strong posterior tuberosity. The ossicle referred to represents the bone called ' cuboid' in the human tarsus. A smaller ossicle, wedged between the astralagus and the metatarsals of the second and third toes is the ' ectocuneiform.' Four toes only are normally developed in the hind-foot of the CrocodiUa ; the fifth is represented by a stunted rudiment of its metatarsal, which is articulated to the cuboid and to the base of the fourth metatarsal. The four normal metatarsals are much longer than the corresponding metacarpals. That of the first or innermost toe is the shortest and strongest ; it supports two phalanges. The other three metatarsals are of nearly equal length, but progressively diminish in thickness from the second to the fourth. The second metatarsal supports three phalanges ; the third four ; and the fourth also has four phalanges, but does not support a claw. The fifth digit is represented by a rudiment of its metatarsal in the form of a flattened triangular plate of bone, attached to the outer side of the cuboid, and slightly curved at its pointed and prominent end. The teeth. — The most readily recognisable character by which the existing Crocodilians are classified and grouped in appropriate genera, are derived from modifications of the dental system. IQ lo OO OO In the Caimans (genus AUifjatof) the teeth vary in number from -^ — i-^ to ^^^r — - : the fourth tooth of the lower jaw is received into a cavity of the alveolar surface of the upper jaw, where it is concealed when the mouth is shut. In PI. 1 C, fig. 2, these pits are shown behind the last premaxillary tooth e, in an eocene Alligator from Hordwell. In old individuals of the existing species of Alligator, the upper jaw is perforated by the large inferior teeth in question, and the fossae are converted into foramina. In the Crocodiles (genus Crocodilus) the fourth tooth in the lower jaw is received into a notch excavated in the side of the alveolar border of the upper jaw, as in fig. 1, PI. 1 C, behind the tooth e, and is visible externally when the mouth is closed, as in PI. ] B, fig. 1. In most Crocodiles, also, the first tooth in the lower jaw perforates the premaxillary bone when the mouth is closed, as in PI. A 2, between the teeth marked a and h. In the two preceding genera the alveolar borders of the jaw have an uneven or wavy contour, and the teeth are of an unequal size. In the Gavials, (genus Gavialis) the teeth are nearly equal in size and similar in form in both jaws, and the first as well as the fourth tooth in the lower jaw, passes into a groove in the margin of the upper jaw when the mouth is closed, PI. 1. In the Alligators and Crocodiles the teeth are more unequal in size, and less regular CROCODILIA. 107 in arrangement, and more diversified in form than in the Gavials : witness the strong thick conical laniary teeth at the fore part of the jaw, as shown in PI. 2 A, figs. 3 and 6, as contrasted with the blunt mammillate summits of the posterior teeth, as shown in Pi. 3 A, fig. 12. The teeth of the Gavial are subequal, most of them are long, slender, pointed, subcompressed from before backwards, with a trenchant edge on the right and left sides, between which a few faint longitudinal ridges traverse the basal part of the enamelled crown. The teeth of both the existing and extinct Crocodilian reptiles consist of a body of compact dentine forming a crown covered by a coat of enamel, and a root invested by a moderately thick layer of cement. The root slightly enlarges, or maintains the same breadth to its base, which is deeply excavated by a conical pulp-cavity extending into the crown, and is commonly either perforated or notched at its concave or inner side. The dentinal tubes in the crown of a fully-developed tooth form short curvatures at their commencement at the surface of the pulp-cavity, and then proceed nearly straight to the periphery of the crown ; they very soon bifurcate, the divisions slightly diverging ; then continuing their course with gentle parallel undulations, they subdivide near the enamel, and terminate in fine and irregular branches, which anastomose generally by the medium of cells. The dentinal tubes send ofl" from both sides, throughout their progress, minute branches into the intervening substance, and terminate in the dentinal cells. These cells are subhexagonal, about -^^ of an inch in diameter, and are traversed by from ten to fourteen of the dentinal tubes ; they are usually arranged in planes parallel with the periphery of the crown, near which they are most conspicuous, and towards which their best defined outline is directed : they combine with the parallel curvatures of the dentinal tubes to form the striae, visible in sections of the teeth by the naked eye, which cause the stratified appearance of the dentine as if it were composed of a succession of superimposed cones. The diameter of the dentinal tube before the first bifurcation is T^Tnrth of an inch, both the trunks and bifurcations of the tubes have interspaces equal to four of their respective diameters. The enamel viewed in a transverse section of the crown presents some delicate striae parallel with its surface, whilst the appearance of fibres vertical to that surface is only to be detected, and these faintly, on the fractured edge. It is a very compact and dense substance ; the dark brownish tint is strongly marked in the middle of the enamel when viewed by transmitted light. The cells with which the fine tubes of the basal cement communicate, are oblong, about -yijVirth of an inch across their long axis, which is transverse to that of the tooth ; the inter-communicating tubes, which radiate from the cells, giving them a stellate figure. I have entered into these particulars of the microscopic texture of the teeth of the Crocodile because it will be seen in the sequel that important modifications of the dental tissues characterise some of the extinct RejMlia. 108 BRITISH FOSSIL REPTILES. In the black Alligator of Guiana the first fourteen teeth of the lower jaw are implanted in distinct sockets, the remaining posterior teeth are lodged close together in a continuous groove, in which the divisions for sockets are faintly indicated by vertical ridges, as in the jaws of the Ichthyosaurs. A thin compact floor of bone separates this groove, and the sockets anterior to it, from the large cavity of the ramus of the jaw ; it is pierced by blood-vessels for the supply of the pulps of the growing teeth and the vascular dentiparous membrane which lines the alveolar cavities. The tooth-germ is developed from the membrane covering the angle between the floor and the inner wall of the socket. It becomes in this situation completely en- veloped by its capsule, and an enamel-organ is formed at the inner surface of the capsule before the young tooth penetrates the interior of the pulp-cavity of its predecessor. The matrix of the young growing tooth affects, by its pressure, the inner wall of the socket, and forms for itself a shallow recess ; at the same time it attacks the side of the base of the contained tooth ; then, gaining a more extensive attachment by its basis and increased size, it penetrates the large pulp-cavity of the previously formed tooth, either by a circular or semicircular perforation. The size of the calcified part of the tooth matrix which has produced the corresponding absorption of the previously formed tooth on the one side, and of the alveolar process on the other, is represented in the second exposed alveolus of the portion of jaw figured in PI. 7.5, fig. 4, of my ' Odontography,' the tooth marked a in that figure, having been displaced and turned round to show the effects of the stimulus of the pressure. The size of the perforation in the tooth, and of the depression in the jaw, proves them to have been, in great partj caused by the soft matrix, exciting dissolution and absorbent action, and not by mere mechanical force. The resistance of the wall of the pulp-cavity having been thus overcome, the growing tooth and its matrix recede from the temporary alveolar depression, and sink into the substance of the pulp contained in the cavity of the fully- formed tooth. As the new tooth grows, the pulp of the old one is removed ; the old tooth itself is next attacked, and the crown being undermined by the absorption of the inner surface of its base, may be broken off by a slight external force, when the point of the new tooth is exposed. The new tooth disembarrasses itself of the cylindrical base of its predecessor, with which it is sheathed, by maintaining the excitement of the absorbent process so long as the cement of the old fang retains any vital connexion with the periosteum of the socket ; but the frail remains of the old cylinder, thus reduced, are sometimes lifted off the socket upon the crown of the new tooth, when they are speedily removed by the action of the jaws. This is, however, the only part of the process which is immediately produced by mechanical force : an attentive observation of the more important pre- vious stages of growth, teaches that the pressure of the growing tooth operates upon the one to be displaced only through the medium of the vital dissolvent and absorbent action which it has excited. CROCODILIA. 109 Most of the stages in the development and succession of the teeth of the Crocodiles are described by Cuvier* with his wonted clearness and accuracy; but the mechanical explanation of the expulsion of the old tooth, which Cuvier adopts from M. Tenon, is opposed by the disproportion of the hard part of the new tooth to the vacuity in the walls of the old one, and by the fact that the matter impressing — viz. the uncalcified part of the tooth-matrix — is less dense than the part impressed. No sooner has the young tooth penetrated the interior of the old one, than another germ begins to be developed from the angle between the base of the young tooth and the inner alveolar process, or in the same relative position as that in which its imme- diate predecessor began to rise, and the processes of succession and displacement are carried on, uninterruptedly, throughout the long life of these cold-blooded carnivorous reptiles. From the period of exclusion from the egg, the teeth of the crocodile succeed each other in the vertical direction ; none are added from behind forwards, like the true molars in Mammalia. It follows, therefore, that the number of the teeth of the cro- codile is as great when it first sees the light as when it has acquired its full size ; and, owing to the rapidity of the succession, the cavity at the base of the fully-formed tooth is never consolidated. The fossil jaws of the extinct Crocodilians demonstrate that the same law regulated the succession of the teeth, at the ancient epochs when those highly organized reptiles prevailed in greatest numbers, and under the most varied generic and specific modi- fications, as at the present period, when they are reduced to a single family, composed of so few and slightly varied species, as to have constituted in the Systema Naturce of Linnaeus, a small fraction of the genus Lacerta. Having completed the analysis of the constituent parts of the framework of the? Crocodilia, which are petrifiable or conservable in a fossil state, and from the study and comparison of which we have to gain our insight into the nature and affinities of the extinct Reptiles, there remains only to be made a few observations on the charac- teristic mode in which the bones are associated together in certain parts of the skeleton in the present order, and especially in the skull. With regard to the trunk, the Crocodilia are distinguished from the Lacertilia and from all other existing orders of Reptiles, by the articulation of the vertebral ribs (pleurapophyses) in the cervical and anterior part of the dorsal segments by a head and tubercle to a parapophysis and diapophysis. As this double joint is associated with a double ventricle of the heart, and as the single articulation of every rib in other Reptiles is associated with a single ventricle of the heart, we may infer a like difference in the structure of the central organ of circulation in the extinct reptiles, manifesting the above-defined modifications in the proximal joints of the ribs. * Op. cit.,pp. 90-3. Q no BRITISH FOSSIL llEPTILES. The sacrum consists of two vertebrae onl}^ in Crocodilia as in Lacertilia : they are modified in the present order, as before described, jj. 89. The skull consists, as we have also seen, of four segments. The hinder or occi- pital surface of the skull presents, in the Crocodilia as in the Lacertilia, a single convex occipital condyle, formed principally by the basioccipital, and not showing the trefoil character which it bears in the Chelonia (PI. 11, fig. 4), in which the exoccipitals con- tribute equal shares to its formation. In the Batrackia, the exoccipitals exclusively form the joint with the atlas, and there are accordingly two condyles. The occipital region of the crocodilian skull is remarkable for its solidity and complete ossification, and for the great extent of the surface which descends below the condyle. (PI. 1 A, fig. 2.) In the Lacertilia, a wide vacuity is left between the mastoid, exoccipital, and par- occipital ; but in the Crocodilia this is reduced to the small depressions or foramina near 3, fig. 2, PL 1 A. The tympanic pedicles (28) extend outwards and downwards, firmly wedged between the paroccipital, mastoid, and squamosal ; in the Lacertians these pedicles are suspended vertically from the point of union of the mastoid and paroccipital. The chief foramen in the occipital region is that called 'foramen magnum' (between 2 and 2, in fig. 2), through which the nervous axis is continued from the skull. On each side of the foramen magnum is a small hole, called ' precondyloid foramen,' for the exit of the hypoglossal nerve. External to this is a larger foramen, marked n in fig. 2, for the transmission of the nervus vagus and a vein. Below this is the ' carotid foramen' c. All these are perforated in the exoccipital. Below the condyle there is usually a foramen, and sometimes two, for the transmission of blood-vessels. Lower down, at the suture between the basioccipital and basisphenoid, is a larger and more constant median foramen, indicated by the dotted line from e t ; it is the bony outlet of a median system of eustachian tubes, peculiar to the Crocodilia. On each side of the median eustachian foramen, and in the same suture, is a smaller foramen, which is the bony orifice of the ordinary lateral eustachian tube. The membranous continuations of the lateral eustachian tubes unite with the shorter continuation from the median tube, and all three terminate by a common valvular aperture, upon the middle line of the faucial palate, behind the posterior or palatal nostril. The large, bony aperture of this nostril is formed by the pterygoids (24 in fig. 2). The carotid canal, c, opens by a short bony tube into the tympanic cavity, and is described as the ' eustachian canal' in the ' Legons d' Anatomic comparce' of Cuvier. The artery crosses the tympanic cavity, and enters a bony canal at its fore part, which conducts to the ' sella turcica' in the interior of the cranium. The median eustachian foramen is described by Cuvier as the ' arterial foramen,'* the canal from which divides and terminates in the ' sella turcica.'! By MM. Bronn, * Ossemens Fossiles, torn, v, pt. ii, p. 133. t lb. p. 78. CROCODILTA. Ill Kaup, and De Blainville, the median Eustachian foramen is contended to be the bony aperture of the posterior nostrils.* The results of the dissections and injections of recent Crocodiles and Alligators, by which I have been able to rectify the discrepant opinions regarding the carotid, eustachian, and naso-palatal foramina, and which have led to the discovery of a third median eustachian canal, or rather system of canals, between the tympanic cavities and fauces, peculiar to the Crocodilian Reptiles, are given In detail in the ' Philosophical Transactions' for 1850. The complexity of the superadded system has doubtless chiefly contributed to mislead the justly-esteemed authorities who have believed that they saw in it characters of the carotid canals or of the posterior nasal passages. The eustachian apparatus in the Crocodilia may be briefly described as follows : From the floor of each tympanic cavity two air-passages are continued ; the canal from the fore part of the cavity extends downwards, backwards, and inwards, in the basisphenoid, which unites with its fellow from the opposite tympanum, to form a short median canal, which descends backwards to the suture between the basisphenoid and the basioccipital, where it joins the median canal formed by the union of the two air-passages from the back part of the floor of the tympanum, which traverse the basioccipital. The common canal formed by the junction of the two median canals descends along the suture to the median foramen e t, fig. 2, PI. 1 A. The air-passage from the back part of the tym- panum, which traverses the basioccipital, swells out into a rhomboidal sinus in its convergent course towards its fellow, and from this sinus is continued the normal lateral eustachian canal, which, on each side, terminates below in the small aperture, external to the median eustachian foramen. That part of the outer surface of the skull which is covered by the common integument is more or less sculptured with wrinkles and pits in the Crocodilia .• the modifications of this pattern are shown in PI. A 2, fig. 1, in the nilotic Crocodile, and in PI. 1 A, in the eocene Crocodile from Hordwell. The flat platform of the upper surface of the cranium is perforated by two large apertures, surrounded by the bones numbered 7, 8, 11, 12; these apertures are the upper outlets of the temporal fossae, divided from the lower and lateral outlets by the conjoined prolongations of the mastoid 8 and postfrontal 12: if ossification were continued thence to the parietal 7, the temporal fossae would be roofed over by bone, as in the Chelones. In old Crocodiles and Alligators there is an approximation to this structure, and the upper temporal apertures are much diminished in size. In the Gavials (PI. 1, fig. 1 a) they remain more widely open, and, in the fossil Gavials of the secondary strata, they are still wider, as seen in fig. 2 « ; by which the structure of the cranium approaches more nearly to that of the Lacertian reptiles, where the temporal fossa is either not divided into an upper and lateral outlet, or is bridged over by a very slender longitudinal bar from the postfrontal to the mastoid. The lateral outlets of the temporal fossae (PI. 1 J, * Abhandlungen iiber die Gavialiirtigen Reptilien der Lias-formation, folio, 1841, pp. 12, 16, 41. 112 BRITISH FOSSIL REPTILES. fig. 1) are divided from the orbits by a bar of bone developed from the postfrontal (12) and malar (26), and against the inner side of the base of whicli the ectopteiygoid abuts ; the posterior boundary of the fossa is made by the tympanic (28) and squamosal (27). The orbits, having the postfronto-malar bar (12, 26) behind, are surrounded in the rest of their circumference by the frontal (11), the prefrontal (14), the lachrymal (73), and the malar (26). The supraorbital or palpebral ossicle is rarely preserved in fossil specimens. The facial or rostral part of the skull anterior to the orbit, is of great extent, broad and flat in the AUigators and some Crocodiles, narrower, rounder, and longer in other Crocodiles, always most narrow, cylindrical, and elongated in the Gavials. The anterior or external nostril is single, and is perforated in the middle of the anterior terminal expansion of the upper jaw. This expansion is least marked in the broad- headed species (compare PL 1 A, fig. 1, with PI. 1 A, fig. 1); in existing Crocodiles and Alligators the points of the nasal bones penetrate its hind border, as at 15, fig. 1, PI. A 2. In the Gavials (PI. 1, fig. 1 a) the nasals («) terminate a long way from the nostril. The Crocodilia resemble the Chelonia in the single median nostril.* In the Lacertilia there is a pair of nostrils, one on each side the median plane, which is occupied by a bridge of bone extending from the usually single premaxillary to the nasals. The plane of the single nostril is almost horizontal in all existing and tertiary Crocodilia. On the inferior or palatal surface of the skull (PL 1 B, fig. 2), the most anterior aperture is the circular prepalatal foramen surrounded by the premaxillaries 22 ; then follows an extensive smooth, horizontal, bony plate, formed by the premaxillaries (22), the maxillaries (21), and the palatines (20). The postpalatal apertures are always large in the Crocodilia, and are bounded by the palatines (20), maxillaries (21), pterygoids (24), and ectopterygoids (25). The posterior aperture of the nostril is formed wholly by the pterygoids ; it is shown in PL 1 a, fig. 3, between the bones marked 24. Behind it is the median and lateral eustachian foramen already described, as belonging rather to the posterior region of the head. Crocodilus TOLiAPicus, Owe7i. PL 2, 2, B, fig. 1. Syn. Crocodile de Sheppy (?), Cuvier. Ossemens Fossiles, 4to, torn, v, pt. ii, p. 165. Crocodilus Spenceui, i?i A, figs. 1, 2, 3, 5, 6. The vertebra, figs. 1, 2, PI. 3 A, is the fourth cervical ; it differs from that of the Crocodilus acufus. Croc. Suchus, and Croc, biporcaius, in the greater breadth and squareness of the base of the hj^papophysis (fig. 2 h), which extends almost to the bases of the parapophyses J9 ; the vertical diameter of the parapophyses is greater in comparison with their antero-posterior extent in the fossil than in tlie above-cited recent Crocodiles ; the neurapophyses are thicker, and terminate in a more rounded border both before and behind ; their bases extend inwards, and meet above the centrum, whilst a narrow groove divides them in the recent Crocodiles above cited ; the length of the centrum is greater in proportion to the height and breadth in the fossil vertebra. In other respects the correspondence is very close, and the modem crocodilian characters are closely repeated. Traces of the suture between the centrum and neurapophysis remain, as shown at n, n, fig. 1 . The diapophysis d, and the upper portion of the neural arch, with the zygapophyses and neural spine, have been broken away ; the borders of the articular ends of the centrum have been worn away. The vertebra (fig. 3, PI. 3 A) is the sixth cervical : in this specimen the base of the hyi^apophysis is contracted laterally and extended antero-posteriorly ; the side of the centrum above the parapophysis {p) has become less concave ; the vertebra has increased R 118 BRITISH FOSSIL REPTILES. more in thickness than in length ; in these changes it corresponds with the modern Crocodiles ; it has been mutilated and worn in almost the same manner and degree as the fourth cervical. The vertebra (figs. 1, 2, PI. 3) is a seventh cervical of a smaller individual of the Crocodilm toUapicus. The hypapophysis has become more compressed and more extended antero-posteriorly ; the parapophysis has become shortened antero-posteriorly, and increased in vertical diameter. The anterior concave surface of the centrum (fig. 1) is more circular, less extended transversely, than in the corresponding vertebra of the recent Crocodiles compared with the fossil. Figures 3, 4, PI. 3, are two views of the eighth cervical of an individual of about the same size as that to which the fourth and sixth cervicals in PL 3 A belong. Fig. 4, exemplifies the same difi'erence which fig. 1 presents in regard to the more circular contour of the anterior concave surface of the centrum as compared with recent Crocodiles ; the bases of the neurapophyses are thicker and more rounded anteriorly ; the neural canal is rather more contracted ; the base of the hypapophysis more extended in the axis of the vertebra (see fig. 3) than in the recent Crocodiles compared. Tlie parapophyses have now risen, as in those Crocodiles, to the suture of the neurapophysis, and the diapophysis springs out at some distance above that suture. Fig. 6, PI. 3, shows the under surface of a dorsal vertebra, in which the hypapophysis ceases to be developed (probably the fourth or fifth). Fig. 5, PI. 30, gives the same view of one of the lumbar vertebras, showing the elongation of the centrum, and the broad bases of the depressed diapophyses ; there is an indication of two longitudinal risings towards the back part of the under surface of the centrum. Figs. 5 and 6, PI. 3 A, give two views of the anterior sacral vertebra of the Crocodilus toUapicus ; it is concave and much expanded transversely at its fore part (fig. 5), flattened and contracted behind. Traces of the suture remain to show the proportion of the anterior articular surface which is formed by the base of the pleurapophysis jo ; and fig. 6 shows the extension of that base from the side of the centrum upon the diapophysis or overhanging base of the neurapophysis ; the under surface of the centrum of this vertebra has a slight median longitudinal rising. Fig. 7, PI. 3, gives a side view of the characteristic, biconvex, anterior caudal vertebra of the Crocodilus toUapicus. Figs. 8, 9, PL 3, give two views of a middle caudal vertebra : in fig. 9 are shown the characteristic hypapophysial ridges extending from the articular surfaces for the hsemapophyses at the hind part of that aspect of the centrum : in fig. 8 the processes of the neural arch are restored in outline ; a thick and low ridge extends from the middle of the side of the centrum to the base of the transverse process which it strengthens, like an underjjropping buttress. CROCODILIA. 119 Vertebrae of the Crocodilus champsoides. Figui'es 7 and 8, PI. 3 A, give two views of the third cervical vertebra of the above- named gavial-hke Crocodile, which vertebra, besides its longer and more slender propor- tions, differs in the smaller size of its hy|}apophysis from the corresponding vertebra in any existing species of Crocodile or Gavial : the process in question being in the form of alow crescentic ridge, as shown at figure 8, between the bases of the parapophyses {p). Both parapophyses terminate by a convex surface, which appears to have been a natural one. Between the parapophysis {p) and diapophysis [d), fig. 7, the side of the centrum is more deeply excavated than in the Crocodilus toliapiciis. The centrum contributes a small part to the base of the diapophysis, as in the third cervical vertebra of modern Crocodiles. The neurapophysis are thinner than in the Croc, toliapiciis, and their bases do not join one another above the centrum. The longitudinal ridge extending from the anterior to the posterior zygapophysis is sharply defined. Figure 4, PI. 3 A, is the first dorsal vertebra of the Crocodilus champsoides, in which, as in existing Crocodiles, the parapophysis {p) has passed almost wholly from the centrum upon the neurapophysis, the diapophysis {d) having been subject to a corresponding ascent. The base of the compressed hypapophysis extends over the anterior third of the middle line of the under surface of the centrum. There is a remarkable transverse constriction at the base of the posterior ball of the centrum, as if a string had been tied round that part when it was soft, and there is no appearance of this groove having been produced by any erosion of the fossil, or being otherwise than natural. The same character is repeated, though with less force, in the posterior dorsal vertebra, fig. 9, PI. 3 A, and, together with the general proportions of the specimen, supports the reference of that vertebra to the Crocodilus champ)soides. There is a slight longitudinal depression at the middle of the side of the centrum near the suture with the neurapophysis («, n). Figure 10 is a side view of the first caudal vertebra of the Crocodilus champsoides : besides being longer and more slender than that vertebra is in the Croc, toliapicus, the inferior surface of the centrum is less concave from before backwards. Tlie evidences of Crocodilian reptiles from the deposits at Sheppy less characteristic of particular species than those above described, are abundant. Mr. Bowerbank possesses numerous rolled and fractured vertebrae, condyloid extremities, and other portions of long bones ; with fragments of jaws and teeth. Mr. J. Whickham Flower, F.G.S., has transmitted to me some fragments of the skull of a Crocodile from Sheppy, including the articular end of the tympanic bone, equalling in size that of a Crocodilus hiporcatas the skull of which measures two feet eight inches in length. Mr. Leifchild, C.E., possesses a considerable portion of the lower jaw of a Crocodile 120 BRITISH FOSSIL REPTILES. of at least equal dimensions, also from Shcppy, showing the angle of union of the rami of tlie lower jaw which corresponds with that in the Crocodllus iolicqncus, PI. 2. In the museum of my esteemed and lamented friend, the late Frederic Dixon, Esq., F.G.S., at Worthing, is preserved a portion of the fossilized skeleton of a Crocodile, from the Eocene clay at Bognor, in Sussex ; it consists of a chain of eight vertebrae, including the lumbar, sacral, and the biconvex first caudal, which are represented of their natural size in tab. xv, of Mr. Dixon's beautiful and valuable work on the ' Geology of Sussex.' A dorso-lateral bony scute adheres to the same mass of clay close to the vertebrae, and doubtless belonged to the same individual. The proportions of the vertebrae agree with those of the Crocodilus toliapicics. This fine specimen was dis- covered, and presented to Mr. Dixon, by the Rev. John Austin, M.A., Rector of Pulbrough, Sussex. Mr. Dixon had also obtained from the same locality a posterior cervical vertebra of a Crocodile, similar in its general characters to those above mentioned, but belonging to a larger individual. The length of the body of this vertebra is two inches and a half. I have examined some remains of Crocodilia from the London Clay at Hackney; but as these also are not sufficiently perfect or characteristic for decided specific determination, no adequate advantage would be obtained by a particular description, or by figures of them. The chief conclusion arrived at from the study of the Crocodilian fossils from the Island of Sheppy has been the proof, by the specimens selected for depiction in the present work, that at least two species of true Crocodile have left their remains in that locality ; that neither of these had a short and broad snout like the Caimans, but that one of them — the Croc, champso'ides — much more nearly resembled the Gavial of the Ganges in the proportion of that part of the skull ; although, in its composition, especially as regards the length and connexions of the nasal bones, it is a true Crocodile. Amongst the existing species of Crocodile the Croc, aciitus of the West Indies offers the nearest approach to the Croc, toliapicus, and the Croc. ScJilc(jeUi of Borneo, most resembles the Croc, champsoides. But there are well-marked characters in both the skull and the vertebrae which specifically distinguish the two fossil Crocodiles of Sheppy from their above-cited nearest existing congeners. Crocodilus Hastings:^, Owen. Plates 1 ^ 1 -8, 1 C,fig. 1 and PI. 1 ^, figs. 2 and 5- ReporU of the British Association, 1847, p. 65. That Crocodiles with proportions of the jaws assigned to the Eocene species noticed in Dr. Buckland's ' Bridgewater Treatise' and especially adapted for grappling wdth strong mammiferous animals, actually existed at that ancient tertiary epoch, and have left their remains in this island, is shown by the singularly perfect fossil skull figured in the above-cited plates. This specimen was discovered by the Marchioness of Hastings, in the Eocene fresh-water deposits of the Hordle Cliffs in Hampshire, which her CROCODILIA. 121 Ladyship has described m the volume of ' Reports of the British Association' above cited, (p. 63). When the specimen was originally exposed, it was in the same extremely fragile and crumbling state as the beautiful carapaces of Trionyx obtained by Lady Hastings from the same locality, and described and figured in the chapter Chelonia ; but thanks to the skill and care with which the noble and accomplished discoverer readjusted and cemented the numerous detached fragments of those specimens, the present unique fossil has been in like manner restored as nearly to its original state as is represented in the plates ; and all the requisite characters for determining the nature and affinities of the species, can now be studied wdth the same facility as in the skulls of existing Crocodiles. If the reader will compare the plates above cited with the section of Cuvier's ' Ossemens Fossiles,' in which the distinctions between the Alligators and Crocodiles are specified,* he will see, (in fig. 1, PI. 1 S) for example, that the fourth tooth or canine of the lower jaw is not received into a circumscribed cavity of the upper jaw, but is applied to a groove upon the side of the upper jaw, and is exposed. Fig. 1, PI. 1 A, shows that the prefrontal (i4) and lachrymal (73) bones, instead' of descending much less upon the facial part of the skull, extend much more, and advance nearer to the end of the muzzle than in any Alligator, or even than in any actual species of broad- nosed Crocodile. The vacuities left between the postfrontal (12), the parietal (7), and the mastoid (s) (PI. 1 A, fig. 1, and PI. 2 B, fig. 3), are as wide as in the skull of a Crocodiiiis biporcatus of equal size, and are larger than in the Alli(/ator Indus or All. sclerops. Fig. 2, PI. 1 B, shows that no part of the vomer is visible between the premaxillaries (22) and maxillaries (21), or elsewhere on the palate. But the palatine expansion of the vomer is not a constant character ; it is wanting, for example, in the Alligator liicius of North America. The palatines (20) are not more advanced in the fossil in question than they are in the true Crocodiles, and their anterior portion does not expand to its anterior truncated termination. The posterior nostril, the entire contour of which is shown in the portion of the skull of the same species figured in PI. 1 A, fig. 3, is longer than it is broad. There is but one character in which the fossil skuU in question differs from the true Crocodile, and agrees with most species of Alligator ; it is in the reception of the two anterior teeth of the lower jaw into cavities of the premaxillaries, shown in * " Les tetes des caimans, outre le nombre des dents, et surtout la manifere dont la quatrieme d'en bas est recue, outre les differences qui dependent de la circonscriptiou totale, se distinguent de celles des Crocodiles proprement dits, 1°, parce que le frontal anterieur et le lacrynial desceudent bcaucoup moins sur le museau ; 2°, en ce que les trous perces a la face superieure du crane, entrele frontal posterieur, le parietal et le mastoidien, y sont beaucoup plus petits, souvent meme y disparaissent tout-i-fait, comme dans le caiman a paupieres osseuses ; 3°, en ce que Ton aper^oit uue partie du vomer dans le palais, entre les interma.iillaires et les maxillaires ; 4°, en ce que les palatins avancent plus dans ce meme palais, et s'y elargissent en avant; 5°, en ce que les narines posterieures y sont plus larges que lougues, etc." (torn, v, pt. ii, p. 105.) 122 BRITISH FOSSIL REPTILES. fig. 2, PI. 1 B, which are not perforated ; so that there are no foramina anterior to the bony nostril, as in PI. A 2, in the bone marked 22. These foramina are not, however, absent in all Alligators ; the skull of the Allic/ator sderops, figured by Cuvier (tom. cit., pi. i, fig. 7), shows them, as do all the species of true Crocodile the skulls of which are figured in the same plate. There is one character by which the Crocodilus Hastingsia differs from all known species of both Crocodile and Alligator : it is that afforded by the broad and short nasal bones (i.'5, fig. I, PI. 1 A), which do not reach the external nostril ; this being formed, as in the Gavials, exclusively by the premaxillaries 22. In the general proportions, however, of the skull in question, especially the great breadth, shortness, and flatness of the obtusely-rounded snout, it resembles that of the Alligators more than that of any known species of true Crocodile, the length from the tympanic condyle to the end of the snout being to the breadth taken at the condyles as 16 to 9. The following are dimensions of the fossil in question : Feet. Inches. Lines. Length of skull from the angle of the lower jaw to the end of the snout Do. from the tympanic condyle to ditto. Do. do. to the orbit Do. from the orbit to the external nostril . Breadth of the skull across the tympauic condyles Do. the orbits Do. the external nostril . Longest diameter of upper temporal aperture Do. the post-palatal vacuities Depth of the lower jaw at the posterior vacuity . Depth of the occipital region ..... The occipital region of the skull (PI. I A, fig. 2), in the proportion of its breadth to the depth of the lateral parts formed by the conjoined paroccipitals (4) and mastoids (s), resembles that of the true Crocodiles rather than that of the Alligators, in which that region is proportionally deeper than in the Crocodiles ; the vertical extent of the supraoccipital is less, and that of the conjoined parts of the exoccipitals above the foramen magnum is greater ; the vertical extent of the descending part of the basioccipital is also greater in proportion to its breadth than in the Alligators. The proportion of the basisphenoid (.5) and of the conjoined parts of the pterygoids (24) which appear in this view (fig. 2), is less than in the Alligators, but is greater than in most Crocodiles, thus presenting an intermediate character ; but the entire exclusion of any part of the posterior nostril from this view is a character of the Alligators, and is due to the horizontal plane of that aperture in them, and to its position in advance of the posterior border of the pterygoids, from which it is partitioned off usually by a bony ridge. The posterior nostril has the same position and aspect in the Crocodilus Hadingsice, and these characters of the posterior nostril are perhaps more distinctive between 1 6 6 1 4 6 5 4 7 9 3 7 4 1 9 4 9 3 4 3 CROCODILTA. 123 Alligator and Crocodile than the shape of the aperture, in which the present fossil differs from botli the Alhgators and most of the Crocodiles with which I have compared it. The backward extension of the exoccipitals and of the basioccipital condyle, is such as to bring both parts into view in looking directly upon the middle of the upper surface of the skull, as in PI. 1 J, fig. 1 . In this character the fossil resembles the Crocodiles more than the Alligators, but the projection is greater than in existing Crocodiles, and equals that in the Sheppy Crocodilus cliamjisoidcs. On the upper surface of the skull a distinctive character has been pointed out by Cuvier in the different proportions of the supra-temporal apertures in the Alligators and Crocodiles. The horizontal platform in which these apertures are perforated, is also square in the Alligators ; the mastoidal angles being less produced outwards and backwards, and the postfrontal angles less rounded off ; this difference is shown in the skulls figured in Cuvier's pi. i, tom. cit. The Croc. Hastuiffsice, both by the obtuseness of the postfrontal angles, and the acuteness and production of the mastoidal angles, resembles the Crocodiles, as well as by the size of the supra-temporal apertures ; these are ovate with the small end turned forwards and a little outwards. Another character may be noticed in the figures of the skulls of the three species of Alligators as compared with those of the three species of Crocodile in Cuvier's pi. i, viz. the larger proportional size of the orbits in the former, in which the orbit much exceeds in size the lateral temporal aperture. In the Alligator niffer, also, I find the orbits enormous, and it is the encroachment of the narrow anterior part of the orbital cavity upon the facial part of the prefrontal and lachrymal, that renders that part of those bones relatively shorter in the Alligators. In the Crocodilus Haslingsm the proportions of the lateral temporal apertures (PI. 1 A, fig. 1, 12, 2C) and orbital (11, u, 73) apertures, are like those in the species of Crocodile in which the orbits are smallest. The extent of the facial part of the prefrontal (14) and lachrymal (73) is greater in the Croc. Ilastinr/sia than in any existing species of true Crocodile. Another characteristic of the present fossil presented by the upper surface of the skull, is the shortness as well as breadth of the nasal bones, and their almost truncate anterior termination at nearly one inch from the external nostril. In all the Alligators' skulls that I have examined or seen figured, the nasal bones are broadest at their posterior third part, and converge to a point anteriorly, where in the Alligator lucius, e. g., they extend across the nasal aperture. The interorbital space is slightly concave in the Crocodilus Hastingsice ; two broad and slightly elevated longitudinal tracts are continued forwards upon the face from the fore part of the orbits ; but they are not developed into ridges, as in the Croc, biporcatus. The maxillaries swell out a little in advance of the middle of the nasals, and then contract to the crocodihan constriction at the suture with the premaxillaries, where the tips of the lower canines appear in the upper view (fig. 1, PL 1 A), and their whole crown is exposed in the side view (fig. 1, PI. 1^. The conjoined parts of the premaxillaries send a short pointed projection into the back part of the exteraal nostril. 124 BRITISH FOSSIL REPTILES. On the under or palatal surface of the skull (PI. 1 B, fig. 2) the niaxillo-prcmaxillary suture runs almost transversely across, as in the Crocodilus rhomhifcr, figured by Cuvier in pi. iii, fig. 2, of the volume above cited. There is no appearance of the vomer upon the palate. The palatal bones (20), though somewhat broader anteriorly, and more abruptly truncate than in any existing Crocodile that I have seen, are more like those bones in the true Crocodiles than in the Alligators. The portion between the post- palatal vacuities is longer and narrower ; the posterior end of the palatines is nar- rower, and the part of the bone anterior to the notch receiving the posterior angle of the palatal plate of the maxillary does not expand in advancing forwards, as it does in the Alligators : in the Alligator niger this expansion is greater than in the All. liicius, and the posterior ends of the palatines are also remarkably expanded, and applied to the anterior borders of the pterj^goids almost as far as their articulation with the ectopterygoids, the postpalatal vacuities not at all encroaching on the pterygoids, as they are seen to do at 24, PI. 1 B, fig. 2, and also in the figure of the Crocodilus rhoinhifcr above cited, and in other true Crocodiles. The form of the pterygoids (24, PI. 1 B, fig. 2) is peculiar in the Crocodilus Hastivgsice -. they are contracted anteriorly, and send forwards a short truncated process to meet the narrow posterior ends of the palatines (20) ; and the same character being repeated in another skull of the same species, from Hordle, also in the collection of Lady Hastings, in which this part of the bony palate (PI. 1 A, fig. 3) is more perfect than in the subject of PI. 1 B, fig. 2, it may be regarded with some confidence as specific. In the Crocodilus chamjjsoides of Slieppy it will be seen, by fig. 2, PI. 2 B, that the pterygoids (24, 24) are not produced where they join the palatines (20). In the Alligators, the posterior border of the conjoined pterygoids is deeply notched behind the posterior nostrils, the angles of the notch being slightly extended backwards : in most Crocodiles, the sides of the notch are so developed that it does not sink deeper than the line of the posterior border of the pterygoids ; and this modification is exaggerated in the Crocodilus Hastingsice (PL 1 A, fig. 3) in which the notch in question is merely the interval between two slender diverging processes from the middle of the back part of the pterygoids, 24. The posterior aperture of the nasal passages is wholly surrounded in the Crocodilus TIastingsia by the horizontal plate of the pterygoids, and has the same position and aspect as in the Alligators ; but its form is heart-shaped, with the apex directed backwards, and the antcro-posterior diameter exceeding the transverse one. I have not met with this form of the posterior nostril in any other species of Crocodilian ; but it is repeated in two individuals of the Croc. liastingsicB, and may be regarded as a specific character. The ectopterygoid, 25, PI. 1 A, fig. 3, PI. 1 B, fig. 2 {d, fig. 2, pi. iii, 'Ossemens Fossiles,' t. V, pt. ii) articulates with a larger proportion of the outer surface of the pterygoids (24) in the Crocodiles than in the Alligators : it agrees with the Crocodiles in the extent of this articulation in the Croc. Ilastingsia. . 22 — 22 Q , The number of teeth in this species is . ,^_., — o4. CROCODILIA. 125 In the upper jaw the fourth, ninth, and tenth are the largest ; and the fifteenth and sixteenth exceed in size those immediately before and behind them. The alveolar border of the jaw increases in depth to form the sockets requisite for firmly lodging these larger teeth, and gives rise to the festooned outline of the jaw, which is found in all Crocodiles and Alligators in proportion as the teeth are unequal in size. The lower jaw presents the same compound structure as that in the Crocodilia, with the general form characteristic of that in the Alligators and in most of the true Crocodiles : the symphysis, e. g. is as short as Crocodilus biporcatus and the Alligator niger, in which it extends as far back as the interval between the fourth and fifth socket. This is the relative position of the back end of the symphysis in a fine and perfect under jaw of the Crocodilus Hasfingsies in the collection of the Marchioness of Hastings. In a portion of the under jaw of apparently the same species of Crocodile, from the same locality, in the collection of Searles Wood, Esq., F. G. S., the symphysis terminates opposite the interval between the third and fourth tooth. The chief distinction observable between the modern Crocodiles and Alligators in the lower jaw is the greater relative size of the vacuity between the angular (30) and surangular (29) pieces, and the greater relative depth of the ramus at that part, in the Alligators. In these characters the lower jaw of the present species more resembles that of the true Crocodiles ; although, as the vacuity in question is somewhat larger, a slight affinity to the Alligator might be inferred from that circumstance. The comparative figures of the hinder third of the mandibular ramus in Plate 1 E, figs. 4, 5, 6, will exemplify the difference in question, and the degree of proximity to the crocodilian and alligatorial characters respectively. With regard to another character deducible from the relation of the backwardly- produced angle of the jaw to the articular surface, the Crocodilus Hasfuigsice more decidedly resembles the Alligator : I allude to the depth of the excavation between the articular cavity (29) and the end of the angle (30), and to the lower or higher level of the angle itself: the fossil jaw (fig. 5) resembles the Alligator (fig. 6) in this respect more than the Crocodile (fig. 4). The alveoli are twenty in number in each ramus of the Crocodilus Hastingsice : the third and fourth are large, of equal size, and close together ; behind these the eleventh, twelfth, and thirteenth are the largest, and the alveolar ridge is raised to support them ; after the seventeenth the summits of the crowns of the teeth become obtuse, and the crowns mammilloid, and divided by a constriction or neck from the fang ; they each, however, have a separate socket, as in the Crocodiles, the septa not being incomplete at the hinder termination of the dental series, as in the Alligator niger figured in my ' Odontography.'* Fig. 3, PI. 2 B, gives a representation, of the natural size, of the cranial platform of a young Crocodilus Hasliiigsice in the collection of Searles Wood, Esq. ; the hemi- spheric depressions in the surface of the bone are more regular, distinct, and relatively * Tom. ii, pi. Ixxv, fig. 3. 126 BRITISH FOSSIL REPTILES. larger, and the interorbital part of the frontal is narrower, concomitantly with the larger proportional eyeballs and orbits of the young animal. The relatively larger supratemporal apertures form another character of nonage ; but there is no ground for deducing a specific distinction from any of the differences observable between this part of the young crocodile's cranium and the corresponding part of that of the more mature specimen (PI. \ J). Alligator Hantoniensis, JFood. Plate 1 C, fig. 2. London Journal of Palseontology and Geology. On reviewing the characters of the skull of the Crocodilus HastingslcE we perceive that they combine to a certain extent those which have been attributed to the genus Crocodilus and the genus Alligator ; in general form it resembles most the latter, but agrees with the former in some of the particulars that have been regarded by Cuvier and other palaeontologists as characteristic of the true Crocodiles. I allude more particularly to the exposed position of the inferior canines when the mouth is shut. Respecting which, however, I am disposed to ask, whether this be truly a distinctive character of importance ? One sees that it needs but a slight extension of ossification from the outer border of the groove to convert it into a pit ; yet the character has never been found to fail as discriminative of the several species of existing Crocodiles and Alligators hitherto determined. It constitutes, however, the only difference between the skulls of the Crocodilus Hastmgsice in the collection of the Marchioness of Hastings and that fine portion of skull now, by the kindness of Mr. Searles Wood, before me, on which he has founded the species named at the head of the present section. So closely, in fact, do those specimens from the same rich locality correspond, that any other comparative view than that given in PI. 1 C appeared superfluous. In both the broad nasal bones terminate at the same distance from the extei'nal nostril, which is accordingly formed exclusively by the premaxillai'ies ; in both, the palate-bones present the same narrow, truncate posterior ends, and the same equal breadth of their anterior portions included between the maxillaries ; only these terminate rather more obliquely in Mr. Wood's specimen, their anterior ends forming together a very obtuse angle directed forwards. But this is comparatively an unimportant difference, and I regard as equally insignifi- cant the slight interruption of the transverse line of the maxillo-premaxillary suture, at the middle part, which will be seen by comparing fig. 2 with fig. 1, in PL 1 C. The teeth are the same in number, arrangement, and proportion in the Alligator Hantoniensis as in the Crocodilus Hastingsice, and the alveolar border of the jaws describes the same sinuous course. Had the complete fossil skull first submitted to my inspection at the meeting of the British Association at Oxford presented the same fossae for the reception of the lower canines which exist in fig. 2, PI. I C, I should have referred it to the Alligators, CROCODILIA. 127 notwithstanding the crocodilian characters of the small orbits, the long facial plates of the prefrontal and lachrymal, the wide supratemporal apertures, the non-expansion of the fore part of the palatines, and the non-appearance of the vomer on the palate, with other minor marks of the like affinity. For all these characters arise out of secondary modifications, and are presented in different degrees in the different species of Crocodile, and are rather of a specific than a generic value. They determine the judgment by the extent of their concurrence rather than by their individual intrinsic worth, and for that reason, therefore, the exposed position of the lower canine in the lateral groove of the upper jaw inclined the balance in favour of a reference of the previously-described fossil to the true Crocodiles. One cannot, indeed, attach any real generic importance to the modification of the upper jaw in relation to the lower canines. In three examples, however, in the collection of the Marchioness of Hastings, the crocodilian modification of this character is repeated, as it is shown in PI. 1 B, fig. 1 ; and we have to choose, therefore, between the conclusion that Mr. Wood's specimen (Pi. 1 C, fig. 2) presents an accidental variety in this respect, or to view the fossae in the upper jaw as indicative of not only a different species but a distinct genus from the Crocodilus Hastingsim. I should be glad to have more evidence on this point, and especially the opportunity of comparing the posterior nostrils, the orbits, the supra- temporal apertures, and the occipital part of the skull of a specimen from Hordle, repeating the alligatorial character of the fossse in the upper jaw for the lower canines. I am disposed to regard this character, notwithstanding its constancy in the living species of Alhgator, as a mere variety in the Hordle fossil ; but pending the acquisition of further evidence, it seems best to record this fossil under the title proposed for it by the able geologist by whom it was discovered. Crocodilus Hastingsi^. Plate 1 1). VertebrcB referable to the Crocodilus Hastingsi^. The fossil crocodilian vertebrae obtained from the Eocene sand at Hordle, notwith- standing the comparatively limited extent of the researches in that interesting formation, are at least as abundant as those which have been discovered at Sheppy, but they do not, as at that locality, indicate two distinct species ; all that have, hitherto, been found belong to one and the same kind of Crocodile, and from their robust proportions, would seem to have come from a species with a short and broad muzzle, like that of the Crocodile or Alligator, the fossil skulls of which have been described. Perhaps the most perfect fossil reptilian vertebra that has hitherto been discovered is the one figured, of the natural size, in PL 1 A figs. 1, 2, and 3. It is the fifth cervical vertebra. As compared with that of the Crocodilus toliapicus (PI. 3 A, figs. 1, 2), which it resembles in size, the hyjiapophysis, hy (fig. 2, PI. I B), is much more compressed, and the under part of the centrum is more extensively and deeply exca- 128 BRITISH FOSSIL REPTILES. vated between it and the parapophyses {p) ; it is also excavated on each side behind the base of the hypapophysis, from which a progressively widening smooth ridge is continued to near the posterior surface of the centrum. The interspace at the side of the vertebra, between the parapophysis and diapophysis, is smaller but deeper in the Crocodilus Hastingsi(B. The neurapophyses meet above the centrum in both ; but in the Crocodilus Hastinf/sice they are thicker anteriorly and thinner at their posterior border, and the neural canal (fig. 2, ti) is more contracted than in the Crocodilus toliapicus. As compared with the cervical vertebra of the Crocodilus champso'ides from Sheppy, the present vertebra differs in the form of the hypapophysis in a greater degree than from the Crocodilus tolicqncus. Fig. 8, PI. 3 A, shows as little as does fig. 2 in the same plate, the median ridge and lateral excavations of the under part of the centrum which charac- terise the present vertebra of the Crocodilus HastingsioE. The Crocodilus cJiampsoides resembles the Crocodilus Hastingsiai in the character of the proportion and depression of that part of the side of the centrum forming the interspace between the par- apophysis and diapophysis ; but the antero-posterior extent of the parapophysis is relatively less in that Sheppy species. The outer surfaces of the neurapophyses in the Crocodilus Hastinxjsice slope or converge towards each other from before backwards, in a much greater degree than in either of the Sheppy species. I have not observed in any recent Crocodile or Alligator the median ridge, continued backwards from the hypapophysis and the lateral depressions, so strongly developed, as in the Crocodilus Hastin(jsice. The fore part of the neurapophyses is relatively thicker in this than in the recent species. The pleurapophyses pi, (figs. 1, 2), are well developed both forwards and backwards, and the latter productions are expanded and excavated above for the reception of the fore part of the succeeding cervical rib. The zygapophyses [z) are thicker at their base, especially the hinder pair, where the base fills up the entire interval between the articular surface and the base of the spine (see fig. 2). There is the usual deep exca- vation at the fore and back part of the base of the spine {ns) for the insertion of the interspinal ligaments. The neural spine is compressed, moderately long, straight and truncate at its summit. Although the hypapophysis maintains its characteristic form with much constancy in the homologous vertebrae of the same species of Crocodile, it varies in different cervical vertebrae of the same individual in certain existing species. It is, for example, shorter and thicker in the third and fourth vertebrae than in the succeeding ones in the Crocodilus acufus ; whilst in the Crocodilus hiporcatus the hypapophysis of the third cervical is more compressed than that of the sixth. The greatest difference is, how- ever, presented, as far as I have yet made the comparison, by the cervical vertebrae of the Alliffcttor lucius, in respect of the hypapophysis, which is broad and short in the third and fourth cervicals, but becomes long and slender in the succeeding ccrvicals. The small vertebral centrum (fig. 4, PI, 1 D) i-esembles, in its broad and stunted CROCODILIA. 129 hypapophysis, that of the third cervical vertebra of the Alhgator, but with an indication of a median rising and lateral depressions, behind that process, Uke those which are more decisively shown in the fifth cervical vertebra of the larger individual of the Croco- dilus HastingsicB, to which species I believe the specimen fig. 4 to belong. It is the homologous vertebra with fig. 8, PI. 3 A, and well illustrates the different proportions of the bones in different species of Crocodile. Fig. 6 gives a view of the anterior surface of the first sacral vertebra of the Crocodilus Ilastingsia : the under surface of the centrum has ceased to develope the median ridge ; the short and thick ribs {-pi) have completely coalesced with both the centrum and neural arch. The anterior concavity has a fuller and more exact elliptical form than that of the Crocodilus toliapicus (fig. 5, PI. 3 A) ; the anterior zygapophyses do not project over the rim of that concavity ; but, like those of the Alligator and Crocodile, they are more transversely extended than in the Gavial. The general proportions of the first caudal vertebra (fig. 7, PI. 1 D) are intermediate between those of the Crocodilus toliapicus (fig. 7, PI. 3) and of the Crocodilus champsoides (fig. 10, PI. 2>A) : the under surface of the centrum is flat, not concave, lengthwise, as in both the Sheppy Crocodiles ; the side of the centrum is irregularly tuberculate, not smooth, and concave lengthwise; the broad and high neural spine is deeply grooved at its fore part : a smaller proportion of the hinder end of the centrum (fig. 5) is occupied by the articular ball than we find in the antecedent vertebrae. As none of the other numerous vertebrae and portions of vertebrae give any indi- cations of a different species from the Crocodilus Hastingsice, or add any material characters to those of that species which have been deduced from the parts of the skeleton already described, I refrain from trespassing on the reader's attention or occupying further space by their description or figures. Genus — Gavialis, Oppel. Gavialis Dixoni, Oiven. Plate 3 B. The characters of the genus Gavialis are much more strongly marked than are those which distinguish the Alligators from the Crocodiles, and leave no ambiguity in the conclusions that may be deduced from them. The present interesting addition to the catalogue of British Fossil Reptiles, is due to the discovery in the Eocene deposits at Bracklesham, by my lamented friend the late Frederic Dixon, Esq., F.G.S., of the remains figured in PI. 3 B. The portions of the lower jaw demonstrate, by the slender pro- portions of the mandibular rami (figs. 1, 5), the extent of the symphysis, the uniform level of the alveolar series, and the nearly equal distance of the sockets of the com- paratively small, slender, and equal-sized teeth, the former existence in England, during the early tertiary periods, of a Crocodilian with the maxillary and dental 130 BRITISH FOSSIL REPTILES. characters of the genus Gavialis. These characters are, however, participated in by some of the extinct Crocodihans of the secondary strata (see PI. 1, fig. 2') ; but in them they coexist with a different type of vertebra from that of the recent and known tertiary Crocodihan genera : it became necessary, therefore, to ascertain what form of vertebra might be so associated with the fossil Gavial-like jaws and teeth in the Bracklesham Eocene deposits, as to justify the conchision that such vertebrae had belonged to the same species as the jaws. Now, the only Crocodilian vertebrse that have yet been found at Bracklesham, so far as I can ascertain, present the procoelian type of articular surfaces of the body (PI. 3^), like that in Mr. Dixon's collection fig. 8. This vertebra answers to the fifth cervical vertebra in the existing Crocodihans, and accords in its proportions with that in the Gangetic Gavial. There are a few indications of specific distinction ; the parapophysis {p) or lower transverse process articulating with the head of the rib, is relatively shorter antero-posteriorly. The broad, rough, neurapophysial sutures {n) meet upon the middle of the upper part of the centrum ; the elsewhere intervening narrow neural tract sinks deeper into the centrum than in the modern Gavial, but is perforated, as in that species, by the two approximated vertical vascular fissures. The hypapophysis {hs) or process from the inferior surface of the centrum, has been broken oiF in the fossil, but it accords in its place and extent of origin with that in the fifth and follo\raig cervical vertebrse of the Gavial. Assuming the fossil procoelian vertebrae from Bracklesham, and the above- described vertebra in particular, to have belonged to the same individual or species as the portions of fossil jaw (figs. 1, 5), then these mandibular and dental fossils must be referred to the genus Gavialis, or to the long-, slender-, and subcylindrical-snouted Crocodilia with procoelian vertebrae. This genus is now represented by one or two species peculiar to the great rivers of India, more especially the Ganges ; and the fossil difi'ers from both the Gavialis ffaiiffeticus, Auct., and from the (perhaps nominal) Gavialis tcnuirostris, Cuv., in the form and relative size of the teeth. The crown (figs. 6, 7) is less slender in the fossil than in the existing Gavials, and less compressed, its transverse section being nearly circular. There are two opposite principal ridges, but they are less marked than in the existing Gavials ; and are placed more obliqviely to the axis of the jaw, i. e., the internal ridge is more forward, and the external one more backward, when the tooth is in its place in the jaw. In the modern Gavial, the opposite ridges, besides being more trenchant, are nearly in the same transverse line. The other longitudinal ridges on the enamel of the fossil teeth, are more numerous, more prominent, and better defined, than in the existing Gavials : the intermediate tracts of enamel present the same fine wrinkles in the fossil as in the existing Gavials' teeth. The two chief portions of jaw (fig. 1, and figs. 4, 5) belong to two individuals of different ages ; indicated by the difference in the breadth and depth of the ramus : both specimens being from the corresponding part of the jaw, viz. where it forms the CROCODILIA. 131 long symphysis characteristic of the Gavials. The specimen (figs. 4, 5) includes a larger proportion of the jaw than the fragment delineated in fig. 1. On comparing the latter fragment of the fossil lower jaw with a specimen of a lower jaw of the Gavialis gangeticm of the same breadth across the symphysial part, at the intervals of the sockets, which breadth is 3 centimeters (1 inch 3 lines), I find that the longitudinal extent of 10 centimeters (near 4 inches) of a ramus of the fossil jaw includes five sockets ; but in the recent Gavial the same extent of jaw includes seven sockets, showing that the teeth are fewer as well as larger in the fossil Gavial, in proportion to the breadth of the jaws. The second portion of the jaw (fig. 2) is from the part where the rami diverge posteriorly from the symphysis, and near the posterior termination of the dentary series. Here the teeth become shorter in proportion to their thickness, and somewhat closer placed together : there is a shallow depression (e) in each interspace of the teeth, for the reception of the crowns of the opposite teeth when the mouth is shut. These depressions are longer, deeper, and better defined in the fossil than in the recent Gavial of the same size. The fragments of jaw and teeth of the fossil Gavial of Bracklesham show examples of young teeth penetrating the base of the old ones, according to the law of succession and shedding of the teeth, which characterises the existing Crocodilia : fig. 2 shows the apex of one of the successional teeth at d ; and fig. 3 d the hollow base of the same incompletely formed tooth seen from below. Besides the fossil jaws, teeth, and vertebrae of the extinct Gavial, a nearly entire femur (fig. 9) of a Crocodilian has been discovered in the Eocene deposits at Bracklesham, which in its proportions, agrees with that bone in the Gavial of the Ganges. Cuvier, in his comparison of the bones of the Gavial with those of the Alligators and true Crocodiles, merely observes, "La forme des os du Gavial ressemble aussi prodigieusement a celle des os du Crocodile, seulement les apophyses epineuses des vertebres sont plus carrees."* With regard to the femur, this bone is more slender in proportion to its length in the Gangetic Gavial, than in the Crocodihis hvporcatus or the AUi