CHELONIA. 



427 



covered with a leathery skin in place of the homy plates which 

 are found in other species. 



In the second section of the Chelonia, in which the limbs are 

 adapted for an amphibious life, are the Mud-turtles or Soft 

 Tortoises {Trionycidm), and the Terrapins {Emydidce). In the 

 TrionyddcR the development, of the carapace is imperfect, the 

 ribs being expanded and united to one another only near their 

 bases, and leaving apertures near their extremities. The 

 entire carapace is covered by a smooth leathery skin, and the 

 horny jaws are furnished with fleshy lips. All the Trionycidce 

 inhabit fresh water and are carnivorous in their habits. Good 

 examples are found in the Soft-shelled Turtle {Trionyx ferox), 



Fig. 165.— Hawk's-bill Turtle (C/UloKia imbricata)—^iti^T Bell. 



and the large and fierce Snapping Turtle {Chelydra serpentina) 

 of the United States ; but other species are found in Egypt 

 and in the East Indies. The Terrapins {Emys) have a homy 

 beak, and have the shield covered with epidermic plates. They 

 are inhabitants of fresh water, and are most of them natives of 

 America. 



The third section of the Chelonia comprises only the Land 

 Tortoises (Testudinidce), in which the limbs are adapted for ter- 

 restrial progression, and the feet are furnished with short nails. 

 The carapace is strongly convex, and is covered by horny epi- 

 dermic plates ; the head, limbs, and tail can be completely re- 

 tracted within the carapace. Though capable of swimming, 

 the Tortoises are really terrestrial animals, and are strictly 



