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Show 1873.] DR. J. E. GRAY ON THE GENERA OF TURTLES. 405 rhombic, rather broader than long, and the second one is ovate, linear, three times as long as broad. This bone does not nearly reach the front edge of the caudal marginal bone, nor does it do so in much larger specimens (as, for instance, the skeleton in the Museum), while it does in specimens of Chelonia in a less-developed state. In a specimen in the Museum, 8 in. long, the front odd bone has become much broader and band-like, and the hinder bone broader, becoming gradually narrower in front, assuming an elongate triangular shape, and reaching the edge of the caudal plates ; and it appears to grow wider as this angle increases in size, having rather concave sides in the younger specimens. I formerly thought that the shape of this bone would distinguish the two presumed species ; but the examination of a large number of specimens of all sizes and ages makes m e have less faith in the character for even separating the younger specimens. M M . Dumeril and Bibron, in the ' Erpetologie Generale,' vol. i. p. 25, t. ii., give a representation of the skeleton, which they call " Chelone'e Caouane," which either does not represent this species or is very incorrect. Indeed I do not know from what species it could have been taken. Can it be from a specimen made up of bones of several species ? The head is much slenderer than that of C. caouana; it is slender and acute in front, like that of Chelonia imbricata. The ribs are only dilated about two thirds of the length, showing that it is from a young specimen; yet the two hinder central bones between the last pair of ribs and the margin are broad, dilated and oblong, and united to the front edge of the hinder marginal bones, very unlike these bones in a young Loggerhead, where they are oblong, longitudinal, thick, and do not reach the marginal bones. Professor Owen, in his ' Monograph of the Fossil Reptilia of the London Clay,' gives the figures of the bones in a front and back view of the dorsal shield of this species and the sternum (pp. 3, 4, f. 1-3). As is his custom, he gives the name of entosternal to the front median piece, episternal to the anterior pair of sternal bones, hyosternal to the second, hyposternal to the third, and to the posterior pair xiphisternal (p. 4); and Professor Huxley, in his * Manual of Anatomy,' p. 202, f. 64, changes the names of these bones to interclavicle, clavicles, hypoplastron, and xiphiplastron. Chelonia subcarinata of Owen's ' Fossil Reptilia of the London Clay,' t. viii., seems nearly allied to this genus; but I should doubt several of the fossils (as C. breviceps and C. longiceps) belonging to it; at least, if they are marine Turtles, they belong to a group quite distinct from any of the existing forms. Tribe 2. LEPIDOCHELYINA. The jaws very strong, the lower one very acute and strongly bent up in front. Costal shields seven on each side ; the first smallest, the fourth, fifth, sixth, and seventh very narrow. The nuchal shield as-wide as the first vertebral. The alveolar surface of the upper beak |
