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Show 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 expanded, ovate-lanceolate, rather contracted before, then 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 tbe 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 |