48 GUIDE TO REPTILES AND AMPHIBIANS. 



skull is completely open, and the tail is short, with the bodies of the 

 vertebrje cupped in front. Some of the neural plates of the carapace 

 are hidden by the costals meeting in the middle line. Inframarginal 

 shields are present, but do not completely cut off the marginals from 

 the abdominals. In some species, the plastron has two transverse 

 hinges, so that the shell can be completely closed. 



The Burmese Casked Terrapin {Platy sternum megacephalum, 68), 

 representing the family Platydernido!, differs from the three pre- 

 ceding families by the absence of rib-like processes to the nuchal bone 

 of the carapace. In this respect it agrees with the Testudmidce, from 

 which it is distinguished by the presence of inframarginal shields 

 between the marginal and the abdominal shields of the plastron. The 

 head is very large, and the temporal region of the skull completely 

 roofed over by bone, in a manner unknown in any other Terrapin. 

 The tail is long, with the articular ends of most of the vertebrae 

 cupped behind. Except that it is aquatic, nothing is known of the 

 habits of this rare and curious Terrapin. 



Cases 6 7. In the more typical Tortoises and Terrapins, constituting the large 

 family Testudinidm (78-175)? the nuchal bone of the carapace lacks 

 rib-like processes ; and, owing to the absence of inframarginals, 

 the abdominal shields of the large plastron abut on the marginals. 

 The head, limbs, and tail can be drawn within the shell ; the 

 temporal region of the skull is open, and the articular ends of the 

 vertebrae of the short tail are cupped in front. From the terrestrial 

 herbivorous Tortoises to the aquatic carnivorous Batagurs there 

 is a transition through the Terrapins. The former have the shell 

 vaulted and lay spherical eggs ; while in all the aquatic forms the 

 shell is depressed, the feet are webbed and have longer claws, and 

 the eggs are oval. 



Case 6. The Hinged Tortoises (Cinyxis, 141, 142) of Tropical Africa are 



unique in having the hinder part of the carapace movable, the hinge 

 passing between the 7th and Sth mai-ginal and the 4th and 5th costal 

 plates. There is no hinge in the plastron. In some species the margins 

 of the carapace are smooth, but in others they [are serrated and turned 

 up. Of the latter type is Cmyxis erosa (142), a species further remark- 

 able for the absence of a nuchal shield to the carapace, and the prolon- 

 gation of the front of the plastron, which forms a fork, covered by the 

 intergular shields. This species lives on vegetable substances, and is 

 said to be partly aquatic, but G. helUana (141) is believed to be entirely 

 terrestrial. The Spider-Tortoise {Pyxis arachnoides, 143) of Mada- 

 gascar is a purely terrestrial species, without any joint in the 



