230 WATER REPTILES OF THE PAST AND PRESENT 



(Caretta), and the loggerhead (Eretmochelys [Fig. 119]) are the best 

 known. They are all thoroughly aquatic in habit, and of large 

 size, from three to five feet in length. The carapace is heart- 

 shaped, and reduced, that is, with large openings between the 

 ribs; the plastron also is reduced and loosely united to the carapace. 

 The neck is short and the head is not retractile within the shell. 

 The temporal region of the skull is roofed over. The four legs 

 form large and powerful flippers, and the hind legs are relatively 

 small. The body is flattened and the tail is small. The aquatic 



Fig. 119. — Eretmochelys, loggerhead turtle. (By permission of the New York 

 Zoological Society.) 



characters of the limbs are seen especially in the broad and strong 

 humerus, with the radial crest for the attachment of powerful 

 muscles situated far down on the shaft; in the relative shortness 

 of the radius and ulna, and the large size of the latter bone; in the 

 flattened carpal bones; and in the great elongation of the digits 

 and the absence of all but one or two of the claws. Unlike the 

 leather-back turtle and the Cretaceous sea-turtles, the carapace 

 and plastron are completely covered with horny shields, from which 

 indeed the tortoise shell of commerce is derived. Except the green 

 turtle, all members of the family are carnivorous. 



