paces have a shagreen or pitted surface, closely resembling the granulated plates under examination; but in the latter there are deep grooves on the sculptured surface, showing that the original was protected by scutes of tortoise-shell, as in the other tribes of Chelonia. "In the rib" (placed on the lowest shelf in Case A.') "these imprints are very distinct, and it is observable that this costal plate, instead of being nearly of an equal width throughout, as in the freshwater and marine turtles, gradually enlarges till one termination is twice as wide as the other. This is a character observable in the land tortoises only, and therefore presents another anomaly in the structure of the fossil animal. From the slight degree of convexity of this rib, it is clear that the original was of a flattened form, like the common turtle, Testudo mydas; its shagreened surface proves its analogy to Trionyx; but the imprints of scales show that it cannot be identified with any recent species. Among the numerous portions of the osseous border of the carapace found in Tilgate Forest, we have not observed any with a shagreen surface; a negative proof that the fossil, like the recent Trionyx, was destitute of that appendage." "2 Specimens far more perfect have since been met with; some of which are in the collection of Sir P. Egerton, and described in "Brit. Assoc. Reports." According to the present state of our knowledge of this remarkable type of freshwater turtles, the carapace was very flat and large, and its surface rugous, as in the Trionyces, but covered with dermal scutes, as in the Emydians: it therefore had not the soft integument of the existing Chelonians, to which it is otherwise nearly related. Except in having a defensive coat of tortoise-shell, the Tretosternum Bakewelli, with its sculptured carapace and rudimentary marginal plates, and unossified centre of its 1 Figured in "Foss. Tilg. Forest," Pl. VI. fig. 1. 2 "Fossils of Tilgate Forest," pp. 60, 61. The paleontologist engaged in establishing the nomenclature of British Fossils, will remark that the above quotation is from a work published in 1827; and that the distinctive characters are sufficiently pointed out to warrant the author in assigning a specific name, six years afterwards ("Geol. S. E. of England," p. 255), to a fossil exhumed from the strata with his own hands, and described and figured in his works alone. plastron, must have closely resembled the existing species of Trionyces; and doubtless, like its modern prototypes, inhabited muddy deltas and estuaries, and preyed on the eggs and young of the large reptiles, and the soft bodies of the mollusks, with whose remains its bones are associated in the strata of Tilgate Forest.' 1 The TRETOSTERNUM BAKEWELLI is described as T. punctatum by Professor Owen in his "Report on British Fossil Reptiles," 1841; with the following remark:-" Portions of ribs of the Tretosternum punctatum, which from their specific punctation and sculpturing of the outer surface have been referred to the genus Trionyx, have been discovered by Dr. Mantell in the Wealden of Tilgate, Illustrations of the Geology of Sussex,' 4to, Pl. VI. figs. 1, 3, 5." Not the slightest allusion is made to my having figured and clearly pointed out the remarkable characters of this extinct Chelonian, many years before Professor Owen had written a single line on any paleontological subject. As the original discoverer and interpreter of this Turtle, I proposed to distinguish it by the specific name Bakewelli ("Geology S. E. of England," p. 255), as a tribute of respect to the late Mr. Robert Bakewell, the eminent geologist, whose "Introduction" was one of the earliest and ablest English works for the student in geology. With a melancholy pleasure I once more associate the name of my lamented friend with a department of paleontology in which he felt peculiarly interested: a privilege, "which, besides the claim of priority, is the honest result of labour devoted to the elucidation of the subject."* * (Quoted from Professor Owen's Brit. Assoc. Report, p. 163.) CHAPTER III. PART III. FOSSIL BATRACHIANS AND SAURIANS. INTRODUCTORY-TEETH OF REPTILES-VERTEBRE OF REPTILES-BICONVEX CAUDAL VERTEBRA-SWANAGE CROCODILE-GEOSAURUS-MACROSPONDYLUS CROCODILUS TOLIA PICUS - CROCODILUS SPENCERI TELEOSAURUS PRISCUS-TELEOSAURUS CHAPMANNI-ENINGEN SALAMANDER-PTERODACTYLES -MOSASAURUS-POLYPTYCHODON. INTRODUCTORY REMARKS.-The fossil reptilian remains we have now to examine, consist of the bones of the skeleton, either detached, or imbedded in the rock somewhat in their original relative position,―of the osseous dermal scutes and spines, which in certain gigantic extinct saurians are greatly developed, of the bony sclerotic plates of the organs of vision, and, very rarely, of the cartilaginous expansions and dermal integuments of the paddles and other parts in a carbonized state. These softer tissues appear, in some instances, to have been converted into adipocire, and subsequently permeated by mineral matter. : The Gallery contains examples, more or less illustrative, of species and genera of the following orders of the class Reptilia, viz. 1. Batrachians, or the Frog-tribe; 2. Ophidians, or Serpents; 3. Lacertians, or Lizards; 4. Enaliosaurians, or marine Lizards; 5. Pterosaurians, or flying Lizards; 6. Crocodilians; 7. Dinosaurians, or extinct colossal Lizards. In the "Medals of Creation," I have given a concise exposition of the most important and easily recognisable characters of the bones and teeth, and other parts of these animals, that are met with in a fossil state, for the guidance of the collector unacquainted with the rudiments of osteology; and to that 1 Vol. ii. chap. xvii. pp. 688-707. work I must refer the general reader desirous of acquiring more particular information respecting the specimens to be reviewed in the present chapter: for anatomical details, and explanations of all the technical terms employed to designate the respective parts, would extend this volume beyond the limits of a hand-book. TEETH OF REPTILES.-The teeth, from their dense structure, are the most durable parts of the skeleton, and these organs occur even in rocks of immense antiquity, in the most beautiful state of preservation; and the various modifications of form and structure, and implantation in the jaws, observable in the existing tribes, are found in the extinct races.' They exhibit considerable diversity of shape, but the characteristic type is that of a simple cone, with either a rounded or pointed apex, and a single fang; for no known reptile, whether fossil or recent, has a tooth with the base terminating in more than one root, and that is never bifurcated. These dental organs are only fitted for seizing and retaining the prey or food; for no living reptiles have the power of performing mastication. In the Crocodile the tooth has a cylindrical shank, and a conical, longitudinally striated, enamelled crown, with a ridge on each side. In the Hyloosaurus, the shank is cylindrical, and the crown expanded and lanceolate, with blunt margins; in the Megalosaurus the tooth is laterally compressed, trenchant, and bent backwards like a sabre, with serrated edges; in the Iguanodon the shank is subcylindrical, and the crown of a prismatic form, greatly expanded, with broad denticulated edges, and a few longitudinal ridges in front; in the Serpents, the teeth are very long and pointed; in the Lizards, may be seen every modification of the conical form, down to a mere hemispherical tubercle or plate. The Turtles are edentulous, i.e. destitute of teeth; their masticating organs consisting of the horny trenchant sheaths with which the jaws are covered. There are five essential modifications in the mode of 1 Teeth of Reptiles.-See "Medals of Creation," vol. ii. p. 688. Vertebra of Reptiles.-Ibid. p. 695. Sacrum, &c.-Ibid. p. 699. Dermal bones.-Ibid. p. 701. M implantation of the teeth, viz.: 1, in distinct sockets, as in Crocodiles; 2, in a continuous groove or furrow, as in the Ichthyosauri; 3, attached laterally by the shank to the alveolar parapet, as in the Iguanas (pleurodonts); 4, anchylosed to the base of a shallow socket, (thecodonts); and 5, attached to an osseous support without sockets or an alveolar parapet (acrodonts), as in the Mosasaurus. The compound structure of the lower jaw of reptiles is also peculiar; there are six distinct bones on each side, and these elements undergo various modifications of form and arrangement in the respective families. VERTEBRA OF REPTILES.-The vertebræ, as the elements which form the spine are termed, are the most numerous and important parts of the skeletons of the extinct reptiles, that come under the observation of the palæontologist, and which present in the gigantic terrestrial saurians, extraordinary deviations from the homologous bones in the existing species. Unfortunately, connected series of vertebræ are but rarely met with in the fluviatile deposits in which the exuviæ of the most remarkable land lizards occur; and it is, therefore, oftentimes extremely difficult to determine whether cervical, dorsal, and caudal vertebræ, discovered apart from each other in the rocks, belong to a spinal column typical of one species or genus, or to several genera. Hence specific and generic distinctions founded on isolated bones, can only be admitted as provisional; for in more than one instance different parts of the same vertebral column have been made the basis of three distinct genera; and, on the other hand, a supposed generic vertebral character not unfrequently proves to be distributed through an entire family of saurians. The fragmentary and isolated condition of the vertebræ imbedded in the Wealden strata of the South-East of England, is a sufficient excuse for error in the interpretation of a piece of bone, or in the reference of an entire bone to a particular species or genus. My own mistakes in this respect I have always unreservedly pointed out; and it is much to be regretted that other labourers in the same department of natural history, of far higher pretensions, do not imitate the noble example of the illustrious Cuvier, and admit and correct the errors into which they have fallen by the ascription of specific and generic distinctions without sufficient |