1873.] DR. J. E. GRAY ON THE GENERA OF TURTLES. 397 



a ridge near its hinder margin, having a longitudinal keel across the 

 hinder half of the concave surface. 



The palate behind the nostrils in the skull is rather concave, and 

 diverges behind into a groove, produced by the elevated margin of 

 the basioccipital and basisphenoid bone. 



1. Caretta. 

 1. Caretta imbricata, Gray, Cat. Tort. p. 74. 



The outer side of the head showing the shields and the upper part 

 of the skull is figured by Temminck in the ' Fauna Japonica,' t. v. & 

 vi. The band of shields at the back edge of the orbit contains three, 

 one being below between the other two and the back margin of the 

 jaw. Temminck's figure of the head of C. imbricata in the ' Fauna 

 Japonica,' t. v. f. 1, does not give a correct idea of the shields of the 

 head as they usually are ; the frontal and parietal plates are united 

 into one, and the soft naked space between the nostrils and the frontal 

 plate is figured to represent a pair of plates. 



In a skeleton of this genus in the British Museum, with the dorsal 

 shield 7 in. long, the hinder central bone of the dorsal disk is ex- 

 panded, ovate-lanceolate, rather contracted before, (hen slightly 

 dilated, and gradually narrowed behind for more than half its length, 

 when it reaches the front edge of the hinder marginal bones. It is 

 keeled on the back as on the vertebral plates. The front of the two 

 hinder central bones is band- like, nearly as broad as the dilatation 

 of the last rib, and narrower in front. 



In a second skeleton in the British Museum, with the dorsal shell 

 lOf in. long, the last bone is rather broader and more ovate. 



2. Onychochelys, Gray, Hand-list, p. 93. 



The beak and shields of the head like those of Caretta imbricata, 

 but the occipital shields larger and longer, the beak more compressed, 

 and the end produced and bent down in the centre. Dorsal shields 

 covered with simple, thin, flat, not thick, imbricate plates. Costal 

 shields 4.4. Front fin with a very large claw to the first, and a small 

 claw to the second finger. The front lateral sternal bones with one 

 acute lobe on the left side, and two acute lobes on the right side of the 

 inner edge directed straight across ; hinder lateral bones with three 

 or four acute diverging lobes on the inner edge, the hinder lobes 

 being rather directed backwards ; the styliform process of the front 

 odd bone elongate or slender. 



This genus is very like Caretta ; but the upper beak is larger and 

 bent down at the end in front, and not truncated as in Caretta ; and 

 the lower beak is also larger and stronger, and the lateral shields on 

 the side of the lower jaw not quite so large. All the plates on the 

 dorsal shield are thin, and not at all produced on the hinder edge. 

 The front vertebral plate is very broad and triangular, much broader 

 than long, and slightly truncated at the front lateral edges ; the 

 second, third, and fourth vertebral plates are hexagonal, contracted 

 on the hinder lateral edges ; the hinder vertebral plate is elongate 



