REPTILES 239 



Family 2. Chelydridae.^ — Snapping turtles. Body large, high in 

 front; carapace rough and tuberculate, and with 24 marginal plates; 

 plastron small, cruciform and composed of 10 plates, besides the 2 

 narrow bridges; head, neck and tail very large; jaws powerful and 

 hooked; toes 5-5, with small webs; claws 5-4: 4 species, 3 in the United 

 States; the largest turtles in the country (except the marine turtles), 

 noted for their ferocity and voracity; aquatic, living on fish, water- 

 birds and other animals ; flesh valued for food. 



Key to the Genera of Chelydridae 



ai Head covered with a soft skin i. Chelydra. 



ao Head covered with symmetrical plates 2. Macrochelys. 



1. Chelydra Schweigger. Carapace with 3 blunt keels, more or less 

 pronounced, growing less so with age; tail very long, with 2 rows of 

 scales beneath; eyes superior in position: 3 species, i in Central America. 



C. serpentina (L.). Common snapper. Length 700 mm. or more; 

 length of carapace 300 mm.; width 260 mm.; weight 30 lbs. or more; 

 2 chin barbels; a row of large compressed tubercles on the upper surface 

 of the tail (Fig. 129); eggs spherical, 25 mm. in diameter, about 25 in 

 number: North America, east of the Rockies, from Canada to the Gulf; 

 common. 



C. osceola Stejneger. Similar to C. serpentina, but with 4 chin 

 barbels and 4 rows of nearly equal tubercles on the upper surface of 

 the tail: Florida. 



2. Macrochelys Gray. Head very large and covered above with 

 plates; tail with small scales beneath; eyes lateral in position; carapace 

 with 3 very prominent tuberculated ridges: i species. 



M. temmincki (Holbrook). AUigator snapper. Length 1,000 mm.; 

 length of carapace 620 mm.; width 530 mm.; weight 120 lbs.; eggs 35 

 mm. in diameter: Gulf States; northward in the Mississippi Valley 

 into northern ]Missouri. 



Family 3. Testudinidae. — Pond and land turtles. Carapace ovate 

 and with flaring edges (Fig. 131) and either depressed or more or less 

 strongly convex, and covered with 5 dorsals, 4 pairs of costals and 25 

 marginals; plastron covered with 12 plates, and of large size and firmly 

 joined with the carapace by wide bridges, and in some species with a 

 movable anterior lobe enabling the animal to close its shell; toes 5-4; 

 eggs elHptical: about 80 species, 30 species in the United States; many 

 species are used for food. 



