EEPTILIA. 



195 



plates " beneath, tliem. They are, therefore, twenty-four or 

 twenty-six in number, the anterior scute in the middle line 

 being distinguished by the epithet of " nuchal," while the 

 corresponding scute behind is termed " pygal." 



Fig. 550. — Carapace of the Loggerhead Turtle (Clielo7ic caoiianna), viewed from above 

 (after Owen). In this form, the ribs are separate and free towards their extremities, and 

 the osseous portions of the carapace are indicated by the light lines, while the epidermic 

 plates are marked out by dark lines, n, n. The first and last of the median series of "neural 

 plates ; " c, c, The expanded ribs or " costal plates ; " ro, vi, The first " marginal plate " on 

 each side ; nu, Nuchal plate ; j)j/, Pygal plate ; v, v, Median series of epidermal plates, or 

 ' ' vertebral scutes. " 



The only remaining points connected with the skeleton 

 which may be just noticed are that the scapular and pelvic 

 arches, supporting respectively the fore and hind limbs, are 

 placed within the carapace ; and that, as in the Crocodilia, 

 clavicles are wanting. The three anterior pieces of the plas- 

 tron may, however, represent an interclavicle and clavicles. 



From the aquatic habits of many of the members of this 

 order they are by no means uncommon in the fossil con- 

 dition. The Turtles frequent the sea, and thus come natu- 



