36 REPTILES. 



Fam. III. Chelydes, (Chelidid^;). 



Head much depressed, broad, covered with a soft skin or hard 

 shields: nostrils elongate, tubular: eyes superior: jaws horny. 

 Neck long, broad, contractile, bent under the side of the shell in 

 repose. Feet webbed. Toes 5-5, deeply webbed, with a lobe be- 

 tween each claw. Claws 5-5, 5-4 or 4-4, elongate, acute. Shell de- 

 pressed, covered with horny shields; caudal pair always separate. 

 Sternum attached to the thorax by a short bony suture, covered 

 with the outer ends of the pectoral and abdominal plates, and with 

 an additional intergular plate in front. The axillary and ingui- 

 nal plates very small or none. Pelvis large, united to the verte- 

 bra and the hinder lobe of the sternum, leaving a scar. Living 

 in ponds and rivers, in warm climates. Eating flesh ; feeding on- 

 ly in the water : swimming with their whole shell under water. 



Synopsis of the Genera. 



A. Head moderate, flat. Jaws naked. Intergular plate marginal. 



a. Toes 5-5. Head shielded. 



1. Sternotherus. Front lobe of the sternum mobile, with a 



long internal process on each side. 



2. Pelomedusa. Front lobe of the sternum fixed. 



b. Toes 5-4. Head with a thin skin or subshielded. 



3. Hydraspis. Shell depressed, thin, light, sides revolute : front 

 edge of thorax and sternum dilated. 



4. Chelymys. Shell convex, very solid, strengthened with two 



compressed diverging bony folds in front, sides revolute. 



5. Phrynops. Shell rather depressed, light, sides expanded ; 

 hinder lobe of the sternum narrowed. 



B. Head large or very large. 



c. Toes 4-4. Head flat, depressed. Jaws naked. Chin not bearded. 



6. Chelodina. Intergular plate intermarginal : nuchal plate 

 small. 



7. HydpvOmedusa. Intergular plate marginal : nuchal plate iu- 



termargiual large, like the vertebral. 



d. Toes 5-4. Head flat, much depressed. Jaws covered with fleshy 



lips : chin bearded : intergular plate marginal. 



8. Chelys. 



d. Toes 5-4. Head convex, rounded, covered with hard shields : 



eyes lateral. Jaws naked. 



9. Peltocephalus. Head subquadrangular : upper jaw hooked. 

 Feet slightly webbed 



Podocnemis. Head sub-depressed, with a groove in front : 

 upper jaw slightly arched. Feet broadly webbed. 



