404 DR. J. E. GRAY ON THE GENERA OF TURTLES. [Apr. 1, 



strongly keeled ; but the keels of the costal plates soon entirely disap- 

 pear, and those of the vertebral plates remain for the greater part of 

 the life of the animal. The vertebral plates are as broad as long, 

 or broader in the young specimens ; but they increase in length as 

 compared with their breadth as the animal grows older. 



1. Caouana. 



The superocular plates are three on each side, the front one 

 being the longest, and meeting the plate on the opposite side 

 in front. The two hinder broader than long, with three shields 

 on the back edge of the orbit, the lower one being the largest. 

 The head-plates are very variable : there is generally a plate be- 

 hind the suture of the occipitals ; sometimes it is placed between 

 the pair; sometimes these plates are moderate, at others very small. 

 The frontal plate varies greatly in size. The parietal plate is gene- 

 rally large and simple ; but in one specimen in the British Museum 

 it is divided into two equal plates by a central longitudinal suture. 



The skull of this genus is figured in Cuvier, Oss. Foss. v. t. ii. 

 f. 1-4. 



The shields of the bead figured by Temminck in the ' Fauna 

 Japonica' under the name of C. cephalo, t. iv. f. 1—3, probably be- 

 long to this genus ; but it has a very large central occipital, which is 

 certainly not the normal form of the species which has come under 

 my observation. 



1. Caouana caretta. 



The sternum of Caouana is figured by Cuvier (Oss. Foss. t. xiii. 

 f. 7), but with too few hinder lateral lobes, and by Prof. Owen 

 (Phil. Trans. 1849, p. 153, f. 3) with too many anterior and poste- 

 rior lateral lobes. 



A skeleton of Caouana in the British Museum, with the dorsal 

 shield 1 7 in. long (the dilatation of the ribs being only extended for 

 about two thirds the length of these bones), has the first of the two 

 odd bones between the hinder pair of ribs consolidated with the rest 

 of the disk ; but Prof. Owen, in a specimen apparently about the 

 same size, represents (f. 1, s 10) this bone as band-like, about 

 half as broad again as long, and six-sided. The Museum specimen 

 has an oblong elongate last bone, nearly twice as long as broad, 

 rather broader in front than behind, and slightly constricted a little 

 in front of the hinder margin. It is very thick, strongly keeled on 

 the upperside, with a rounded tubercle at the end of the keel. It 

 does not reach the hinder edge of the two hinder marginal bones. 



This bone is well seen in the younger specimens of the complete 

 animal, and forms a prominence at the end of the dorsal keel ; but 

 I believe it dilates on the sides, as the sides of the ribs dilate in the 

 older specimens, so as to form with the ribs and margin a solid con- 

 tinuous shield. The bone is not well represented in Prof. Owen's 

 diagram. 



In a young specimen 9 in. long, the front odd hinder bone is 



