550 TEXTBOOK OF ZOOLOGY 



Family Testudinidae. — Only three species of turtles found in the 

 United States belong to this family; namely, the gopher tortoise, 

 Berlandier's tortoise, and Agassiz's tortoise. Members of this family 

 are numerous in Africa, on the Galapagos Islands, and in other 

 widely separated localities. How these three species of turtles come 

 to be in North America is a most interesting problem in animal 

 distribution. All three species found in this country are dark brown 

 or black on the carapace, often lighter ventrally. Young individuals 

 usually show a light area in the center of each dorsal scute. Since 

 they are all dry-land turtles, they lack the streamlined form of 

 water dwellers. The most distinct characteristic of our species is 

 a narrow extension of the plastron into a gular process. 



Family Cheloniidae. — This family includes the green turtles, the 

 shell turtles, and the loggerhead turtles. All are marine animals, 

 and show modifications for an aquatic existence in the form of the 

 body and in the modification of feet into flippers. Many members 

 of this family may weigh five hundred pounds, but most specimens 

 seen in the markets weigh much less. 



Family Dermochelidae. — This family contains but one genus with 

 two species. They are commonly known as the leatherback turtles, 

 the trunk turtles, or the harp turtles. Unlike most turtles, they 

 lack the covering of horny scutes, being covered instead with a 

 leathery integument. These are the largest of living turtles. Large 

 individuals may weigh as much as one thousand pounds. 



Suborder Trionychoidea. — Members of this suborder are found in 

 North America, Africa, Asia, and New Guinea. They are among 

 the most aquatic of all land and fresh-water forms. The only occa- 

 sion on which they leave the water is to deposit eggs. 



Family Trionychidae. — This is the only family of the suborder 

 having representatives in North America. It is represented by five 

 species and one subspecies, all in the genus Amy da. All are "soft- 

 shelled" turtles covered with a soft rubberlike skin instead of the 

 horny scutes present on most turtles. The color on the dorsal side is 

 olive brown, while the ventral side is white. Any of these species will 

 bite viciously when angered and can inflict painful wounds. It was 

 probably one of these turtles that gave rise to the belief that a turtle 

 would not loose its hold until it heard thunder. They have a habit 

 of retaining their grip on a victim very tenaciously. 



