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 piates 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 pre- 

 cedents (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. my das, 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 repre- 

 sents. 



Dr. Krauss has kindly sent me the head of a rather larger speci- 

 men of this Turtle, which euables 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 on the 

 two sides of the head are not regular and similar, we may con- 

 sider 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 

 tn 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 



