REPTILES. 



307 



saurus and Pliosaurus from the Jurassic and cretaceous of 

 Europe, America, and New Zealand. 



ORDER III. CHELONIA (TESTUDINATA). 



Recent and fossil reptilia in which the trunk is enclosed in 

 a bony framework, composed of a dorsal carapace and a ven- 

 tral plastron, these parts of dermal and partly of endoskeletal 

 origin ; the quadrate is fixed ; teeth are lacking, the jaws being 

 covered with a horny sheath. The anterior bony nares are 



FIG. 303. Pectoral 

 girdle of Plesiosaurus, 

 after Zittel. c, coracoid; 

 cl, clavicle ; *?, episternum ; 

 s, scapula. 



FIG. 304. Dorsal view of carapace of 

 green turtle, Chelone midas, showing the ribs, 

 RI extending beyond the costal plates, C. M, 

 marginal plates; Ntt y nuchal; Py, pygal 

 plates. From Huxley. 



united, and open at the tip of the snout. A temporal fossa is 

 frequently present. The scapular and pelvic arches are internal 

 to the ribs. The feet have five digits and, while usually fitted 

 for walking and provided with claws, are occasionally modified 

 into flippers. 



The turtles and tortoises are strongly marked off from all 

 other reptiles, the armor surrounding the body being especially 

 characteristic. In most cases head, legs, and tail can be re- 

 tracted into this, and in the box tortoises the plastron is hinged 



