402 DR. J. E. GRAY ON THE GENERA OP TURTLES. [Apr. I, 



shields at the hack 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 com- 

 pared 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 spe- 

 cimen 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 

 b - 6 lbs. 



I think both these skulta 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 be- 

 yond 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 dila- 

 tations 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 



