SURVEY OF VERTEBRATES 



121 



— some land-dwellers, others aquatic — depend upon this rather 

 than speed for protection. In fact a few, like the Box Tortoise, 

 can completely seal themselves up, as it were, between the dorsal 

 carapace and the ventral plastron. The tortoise-shell of com- 

 merce is the horny outer layer of the carapace of the Hawk's 



G D 



Fig. 80. — Turtles. A, Box Tortoise enclosed within carapace and plastron; 

 B, Tortoise-shell Tortoise, Eretmochelys imbricata; C, Snapping Turtle, 

 Chelydra serpentina; D, Mud Turtle, Cinosternum pennsylvanicum. (A from 

 Bamford; B, C, D from Newman, after Lydekker.) 



bill, or Tortoise-shell, Turtle. Probably the protective shell also, 

 in part, accounts for the fact that the jaws of Turtles and Tor- 

 toises are toothless. Never thless, many can inflict severe wounds 

 — witness the beaked jaws of the Snapping Turtle. (Fig. 80.) 



2. Crocodiles and Alligators 



Predatory inhabitants of tropical rivers, Crocodiles and Alli- 

 gators are lizard-like in form with long, gaping jaws well armed 

 with teeth, and with a thick, leathery skin covered with horny 

 scales. Alligator skin has long been popular for the manufacture 

 of leather goods. 



3. Lizards and Snakes 



The Lizards form a highly diversified group, typically with 

 scaly skin and well-developed limbs and long tail. Representative 

 Lizards are the common Iguana, the Gila-monster, and the Horned- 



