TORTOISES. 



3 



Sect II. Shielded Reptiles, (Cataphracta). 



Body covered with square imbedded plates, generally forming 

 a dorsal and ventral shield. The bones of the skull thick, united 

 together into a hard mass, and including the quadrate bones and 

 pterygoid processes. The tongue is short, affixed to the mouth, 

 scarcely exsertible. The lungs are enveloped by a thick perito- 

 neum, which performs the part and has the appearance of a dia- 

 phragm. The vent is round or linear, plaited. The male organ and 

 vagina are simple, the former having only a groove along its up- 

 per edge. Oviparous: the egg covered with a hard shell: the 

 young, when hatched, having a large umbilical slit, which soon 

 disappears. 



Order III. TORTOISES, (CHELONIA). 



The body enclosed in a case, formed of two shields united by 

 their margins, and leaving only the head, neck, limbs and tail free, 

 which are covered with a scaly skin: the upper shield or thorax 

 formed of the ribs more or less dilated on the sides, united toge- 

 ther and adherent to the dorsal vertebrae by a toothed suture, pre- 

 venting any motion ; they are surrounded by a series of bones 

 forming the edge of the shields : the lower shield or sternum is 

 formed of four pair and a central anterior bone. The jaws are 

 toothless, covered with a horny bill, rarely hid by fleshy lips: the 

 upper bill covers the lower like a box. Eyes with distinct eyelids. 

 The drum of the ear visible, nearly superficial. The legs short, 

 thick. Tail conical. The vent is a circular hole. 



Synopsis of the Families. 



1. TestudinidjE. Feet club-shaped; claws 5-4 or 4-4, blunt. 



Caudal shields united into one, incurved. Neck retractile. 



2. Emydid^:. Feet palmated ; claws 5-4 or 4-4, acute. Caudal 

 shields separate. Neck retractile. Pelvis attached to the ver- 

 tebrae only. Sternal shields 11 or 12. 



3. ChelydidjE. Feet palmated ; claws 5-4 or 5-5, acute. Caudal 



shields separate. Neck contractile. Pelvis attached to the ver- 

 tebrae and sternum. Sternal shields 13. 



4. Trionycidid^e. Feet palmated ; claws 3-3, acute. Bones co- 



vered with a soft skin having a flexible margin. 



5. Cheloniad;e. Feet fin-shaped, compressed. 



B 2 



