THE LAND TORTOISES AND TERRAPINS 2423 



while agreeing with the members of the foregoing genus in the pres- 

 ence of a bony temporal arch to the skull, differ by having a well- 

 Terrapins 



marked transverse ligamentous hinge across the middle of the plastron, 



whereby its hinder lobe is rendered movable and capable of more or less completely 

 closing the posterior aperture of the shell. None of the species have a shell of 

 more than eight inches in length. The genus may be subdivided into two groups, 

 each containing three species. In the former, as represented by C. dhor of North- 

 ern India and the Malayan region, the plastron, which is notched behind, cannot 

 completely close the shell; while the hinder margin of the carapace is serrated. In 

 the second group, on the other hand, of which the Amboyna hinged terrapin 

 (C. amboinensis) is a familiar example, the plastron is capable of completely closing 

 the hinder aperture of the shell, while the posterior margin of the carapace is not 

 serrated. These species also have the shell keeled on the back in the young state. 

 In the Amboyna species, as also in C. flavomarginata , the hinder end of the plastron 

 is entire, although in a third (C. trifastiata) it is notched. 



Agreeing with the hinged terrapins in the presence of a transverse 

 ligamentous hinge across the middle of the plastron, by the aid of 

 which the openings of the shell can be closed, the two North- American species of box 

 tortoises, together with all the remaining members of the family, differ from the 

 former in that the hexagonal neural bony plates of the carapace have the shorter 

 of their two lateral surfaces placed anteriorly, instead of posteriorly, this arrange- 

 ment being shown when the shell is stripped. The presence of the hinge in 

 the plastron serves to distinguish the box tortoises from all the members of the sec- 

 ond group, with the exception of the pond tortoises, while from the latter they 

 are separated by the beak being hooked and the absence of a bony temporal arch to 

 the skull. In the box tortoises the head is covered with smooth skin above, the toes 

 having only a rudimental web, and the tail is short. The Carolina box tortoise 

 (Cistudo Carolina) is a somewhat variable species as regards size, the length of the 

 shell ranging from a little over four to somewhat more than five inches. The highly 

 convex carapace is almost hemispherical in shape and is attached to the plastron 

 solely by ligament, so that the whole shell can be completely closed. As a general 

 rule, the upper shell is dark brown or blackish with yellow spots, or brownish yel- 

 low with dark brown spots or rays, while there may be an interrupted yellow streak 

 down the middle of the back. The plastron may be either a uniform dark brown or 

 blackish, or may have irregular yellowish blotches on a ground of the same, while 

 in some instances it is yellowish with dark blotches of variable size. The range of 

 this species embraces the Southern and Southeastern United States and Mexico. In 

 the ornate box tortoise from Nebraska and some neighboring states, the shell is 

 more depressed, and the plastron and carapace are connected by a very short 

 bony bridge, so that the shell cannot be completely closed. The toes, moreover, 

 have no distinct webs. 



The vaulted carapace of the box tortoises, with their abruptly descending 

 hinder profile, together with the rudimentary condition of the webs of the toes, at 

 once proclaim the terrestrial habits of these reptiles, which form, indeed, one of the 

 connecting links between the true tortoises and the fresh-water terrapins. Although 



