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Show 1873.] DR. J. E. GRAY ON THE GENERA OF TURTLES. 401 curve. The horny plates are thin, smooth, worn, and are studded with different-sized Turtle-barnacles (Chelonobia), and also with a large number of common barnacles, especially on the sides of the back, leaving the middle of the dorsal plates bare. The specimen here described was sent to me by Dr. Krauss from Stuttgard, as Chelonia marmorata of Dumeril and Bibron (Erp. Gen. ii. p. 346, t. xxiii. f. 1) ; but it cannot be that species, for they say, " Sous le rapport de la forme, cette espece ne differe pas de la precedente (C. maculosa), elle s'en distingue seulement par son systeme de coloration." He figures the head-shields (t. xxiii. fig. 1 a) as like those of C. mydas, and very different from the head-shields of C. imbricata on the same plate (fig. 2 b), which these are like. I may here remark that their figure of the beak of C. imbricata is so incorrect as to represent this species rather than the true C. imbricata, which is the one that their figure of the back represents. Dr. Krauss has kindly sent me the head of a rather larger specimen of this Turtle, which enables me to describe the alveolar surface of the jaws, which is very different from that of any known Turtle, and confirms the genus. This head has the shields rather different from the specimen originally described; and as the shields ou the two sides of the head are not regular and similar, we may consider them abnormal. There is a narrow strap-shaped shield on the left side and parallel to the outer margin of the large central hinder plate ; but this shield is separate on the hinder half, and united to the central shield on the front half of the right side of that shield. In the same manner the large temporal shield just beside the supraoccipital shield is divided into three shields on the left side, and into two shields on the right side of the head; and the upper shield is longer on the right side than it is on the left: but it is easy for any one to see that these do not alter the character. Tribe 2. CHELONINA. The head is oblong and rounded in front. The lower jaw is strongly dentated on the outer edge, and, except just in front, is strongly striated on the outer surface, and fits into the very high sharp margin of the upper beak, which is also deeply and regularly grooved on its inner margin. The alveolar surface of the upper beak and of the skull beneath it with a narrow diverging ridge on each side nearer the outer than the inner margin, separated by a longitudinal groove in the centre, and with a linear raised granular ridge margining the hinder edge of the alveolar surface. The alveolar surface of the lower beak and jaw with a strongly dentated edge, and a deep triangular concavity within it, divided in half by a central longitudinal ridge, and with a sharp ridge parallel to but some little distance from the hinder margin, the acute ridge and flat hinder space being granular. The horny part of the lower beak triangular, only covering the front end of the jaw. The horny plate on each side large, narrow, and only covering the front two thirds of the narrow prominent lower part of the jaw. The band of PROC. ZOOL. Soc-1873, No. XXVI. 26 |