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Show 404 DR. J. E. GRAY ON THE GENERA OF TURTLES. [Apr. 1, strongly keeled; but the keels of the costal plates soon entirely disappear, 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 behind 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 generally 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 head figured by Temminck in the ' Fauna Japonica' under the name of C. cephalo, t. iv. f. 1-3, probably belong to this genus; but it bas a very large central occipital, which is certainly not the normal form of the species which has come under m y 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 posterior 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 continuous 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 |