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 trian- 

 gular 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 me have less faith in the cha- 

 racter for even separating the younger specimens. 



MM. Dume'ril and Bibron, in the ' Erpetologie Generate,' vol. i. 

 p. 25, t. ii., give a representation of the skeleton, which they call 

 " Chelonee 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 1 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 cen- 

 tral bones between the last pair of ribs and the margin are broad, 

 dilated and oblong, and united to the front edge of the hinder mar- 

 ginal 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 pos- 

 terior 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 



