TORTOISES AND TERRAPINS. 



45 



Fig. 48. 



Upper and Lower views of Skull of Hawksbill Turtle (Chelone imbricata), 

 showing the presence of a secondary floor to the palate and the conse- 

 quent backward position of the posterior nostrils. 



Section THECOPHORA. 

 Sub-order I. — Cryptodira (S-necked Tortoises). 



The Cryptodira, or S-necked Tortoises, which constitute the 

 majority of living Chelonia, are characterised, as already mentioned, 

 by the head being drawn in by an S-like bending of the neck in 

 a vertical plane so that the head occupies the centre of the front of 

 the shell (fig. 55). Unlike the Pleurodira, in which the bones of the 

 pelvis are welded to the upper and lower shells, their bones are free. 

 Specimens are exhibited in case 9 to illustrate the essential differences 

 between the Cryptodira and Pleurodira. 



Of the three living representatives of the family OhelydridcB (75-77), Case 6. 



