CLASS REPTILIA 535 



snout with hooked beak. Examples: Chelydra, 

 Macrochelys (Fig. 444). 



Family 2. Kinosternid^e. — Musk- and Mud-turtles. 

 — Cryptodira possessing a nuchal plate with costi- 

 form processes underlying the marginals ; eight 

 bones in the plastron. Examples : Kinosternon, 

 Aromochelys. 



Family 3. Dermatemydid^e. — Fresh- water Turtles 

 of Southern Mexico and Central America. Crypto- 

 dira with nuchal plate as in Kinosternid^e; nine 

 bones in plastron. Examples: Dermatemys, Stauroty- 

 pus, Claudius. 



Family 4. Platysternid^e. — Cryptodira without costi- 

 form processes on nuchal plate. Examples: Platy- 

 sternum (a single species, P. megacephalum, in Burma, 

 Siam, and China). 



Family 5. Testudinid^e. — Tortoises and most Turtles. — 

 Cryptodira without costiform processes on nuchal 

 plate; lateral temporal arch usually present; no 

 parieto-squamosal arch. Examples: Testudo (Fig. 

 446), Chrysemys (Fig. 445), Emys. 

 Superfamily 2. Cheloniidea (Chelonid^e + Atheca) . — 

 Sea-turtles. — Marine Testudinata with paddle- 

 shaped limbs. 



Family 1. Cheloniid^e. — Four species inhabiting tropical 

 and semitropical seas (Fig. 447). 



Family 2. Dermochelyid^e. — The leathery turtle of 

 tropical and semitropical seas (Fig. 448). 

 Superfamily 3. Pleurodira. — Testudinata with neck 

 bending laterally; pelvis fused with the shell. 



Family 1 . Pelomedusid^e. — Fresh- water Turtles. — • 

 Pleurodira with neck completely retractile within 

 the shell; carapace without nuchal shield; plastron oi 

 eleven bones. Examples: Pelomedusa, Podocnemis, 

 Sternoth&rvs. 



