REPTILES 237 



b2 Shell not covered with horny plates, but with a leathery- 

 skin 4. Trionychidcc. 



aj Limbs in the form of flippers; size very large; sea turtles. 



bi Shell covered with horny plates 5. CheloniidcB. 



bo Shell not covered with horny plates, but with a leathery 



skin 6. DermochelidcB. 



Family I. Kinosternidae. — Mud and musk turtles. Rather small, 

 aquatic turtles with an elongate body; carapace elliptical, with 23 margi- 

 nal plates, usually smooth, without a flaring edge (Fig. 130); plastron 



Fig. 129. — Tail of Chelydra serpentina (from Surface). 



well developed, with movable anterior and posterior lobes, covered 

 with 9 to II plates and joined with the carapace by narrow bridges; 

 toes 5-5; claws 5-4; feet webbed; head pointed; jaws strong: 14 species, 

 all American, 7 in the United States, in a single genus, inhabiting slow 

 streams and muddy ponds, and eating animal food; eggs elliptical; 

 all the species emit a musky odor. 



Kinostemon Spix. Head with a large rhomboidal plate; plastron 

 usually large, with a deep notch behind; tail with a terminal claw: 

 7 species. 



Key to the United States Species of Kinostemon 



ai Plastron very narrow and not covering the soft parts. 



bi Head with yellow stripes K. odorahim. 



bo Head spotted; shell with imbricated plates K. carinatuni. 



ao Plastron larger, covering the soft parts when closed. 



bi Bridge very short, about a third the length of fore lobe of 



plastron A', steindachneri. 



bo Bridge longer, about half the length of fore lobe of plastron. 

 Ci Fore lobe shorter than hind; carapace with 3 yellow 



stripes K. bauri. 



Co Fore lobe as long or longer than hind. 



di Head spotted with yellow K. subrubrum. 



d2 Sides of head bright yellow K. flavescens. 



(h No yellow on head or body A', sonoriense. 



K. odoratum (Latreille). Musk turtle. Carapace 90 mm. long 

 and 60 mm. wide; color brownish, often striped or blotched with a 

 darker color; plastron yellowish 01 brown; head large, with strong jaws; 

 plastron 68 mm. long and 31 mm. wide; side of head with 2 narrow 



