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Show 1873.] DR. J. E. GRAY ON THE GENERA OF TURTLES. 407 each pair of ribs. I thought at first that this might be an individual peculiarity ; but it appears common to the group ; for it is equally well marked in a nearly adult shell, in a younger one about two thirds the length of the former, and in a very young one five inches long. The dorsal shield of this genus is very thin, more like a thin, hard, semitransparent skin than the horny plates usually called tortoise- or turtle-shell; and it allows the sutures of the bone to be seen through it. Fitzinger, in his ' Systema Reptilium,' p. 30, gives two generic names to this species, Lepidochelys olivacea and Thalassochelys olivacea. As I wanted a generic name, I have employed the first name, and given it a proper character; but I have no doubt that it will be quoted as Fitzinger's genus, although his character is not taken from nature. This genus differs from the genera Caouana, Caretta, and Chelonia in the number of head-shields that it possesses. 1. LEPIDOCHELYS OLIVACEA, Gray, Hand-list Tort. p. 91. There is a nearly adult animal and shell of this species in the British Museum. There is also a dorsal shell of a specimen nearly adult, but only 18 inches long, from Cape York, which has elongated vertebral plates like the former specimen. This specimen is peculiar for having six vertebral shields; but the three hinder are very short, the first and sixth being much shorter than broad, and the fifth about as broad as long. They appear to be merely a malformation of the fourth and fifth shields in the more adult specimens. The keel is compressed and very high on the hinder half of the first and second, and only slightly marked on the hinder part of the third, and on the hinder and front part of the fourth and fifth vertebral shields, the position of the two lateral plates being caused by the unusual division of these plates. The hinder or caudal shields are very large, long and square, approaching to what they are in the genus Eremonia. There is also in the British Museum a young specimen of the genus from the Philippine Islands which appears to belong to the species; the back is three-keeled, the keel of the vertebral plates, which are broader than long, being the highest; it has seven costal shields on each side. The sternum is bluntly keeled on each side. The lower beak is rather shorter than in the adult specimen in the British Museum, and it has a narrower elongate plate on each side behind it; but this plate is very unlike the large elongate oblong shield on the side of the jaw of Chelonia. The beak of the lower jaw appears to be smaller than in the adult animal; and in this respect it is something like the genus Caouana, which has the lower beak smaller compared with that of the adult Lepidochelys. In this specimen there is a small square shield interjected between the fourth and fifth vertebral shields. |