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Show 402 DR. J. E. GRAY ON THE GENERA OF TURTLES. [Apr. 1, shields at the back edge of the orbit consisting of four or five shields, one at the lower part of the orbit between the other shields and the margin of the jaw. They seem to vary in number, as in one specimen there are four on one side and five on the other ; but I believe four is the usual number. The skull is not so broad compared with its length as that of the Loggerhead (Caouana). 1. CHELONIA. Temminck represents the side and top of the head and the side and top of the skull of Chelonia viridis (Fauna Japonica, t. iv. & vi.). The sternum is well figured by Cuvier (Oss. Foss. t. xiii. f. 6). The generality of specimens in the British Museum have the hinder part of the base of the skull nearly flat; but there is one skull of a half-grown Turtle which has this part keeled in the middle, and there is a concavity on each side of the middle, and diverging on each side of the triangular prominent basisphenoid bone. This may be the character of one of the species; but I have not the specimen to which the skull belongs, and therefore cannot name it with certainty. There is another small specimen which seems to have this character not quite so much developed; but it is also the odd skull of a Turtle that was "dressed" in 1811, and weighed 66 lbs. I think both these skulls are rather narrower compared with their length than the other skulls, which have this part more flattened. In a dorsal shield of a skeleton of Chelonia viridis in the British Museum, 34 in. long, the hinder of the two odd bones placed beyond and attached to the hinder edge of the dilated part of the last pair of ribs is nearly semilunar, about half as long as broad, with a projecting rounded hinder edge, very short, and band-like on the lateral margin, which is nearly as broad as the back edge of the dilatation of the last or eighth pair of ribs. The front margin is concave. The last odd bone is triangular, as broad as long, with a broad semicircular front edge, and is contracted on the sides in front at the hinder part, and is attached by its tip to the front edge of the two hinder marginal bones. In the older specimens, when the dilatations of the ribs reach the marginal bones, these odd bones do so at the same time, and thus lose their characteristic form. In one specimen with the dorsal shield 4% in. long, which has three straight rays on one side and four on the other, the front odd bone between the last ribs is rhombic, longer than broad, narrower in front; and the second bone is elongate-lanceolate, narrow in front and behind, not reaching the inside of the hinder marginal bone. 1. CHELONIA VIRIDIS. 2. CHELONIA VIRGATA. There appears, by the colouring of the dorsal disk, to be two species of true herbivorous Turtle, C. viridis and C. virgata, Cuv.; and I formerly thought that I had discovered an organic character in the form of the last two central vertebral plates between the |
