CLASS AMPHIBIA 521 



from Texas, and Lithodytes ricordii from Florida. Most of the 

 Cystignathida occur in Mexico and Central and South America. 

 They form a comparatively heterogeneous group and are not 

 easily defined. 



Family 5. ENGYSTOMATID^E. The narrow-mouthed toads 

 as a rule inhabit the tropics. Only three of the seventy or more 

 species are found in the United States. Engystoma carolinense 

 ranges from South Carolina to Florida and west to Texas. Like 

 other members of the family, its head is narrow and pointed and 

 is thus adapted for the capture of ants and other small insects. 



Family 6. RANID^E. The true frogs occur in all parts of 

 the globe except Australia, New Zealand, and southern South 

 America. Only one genus, Rana, and about seventeen species 

 are found in North America. Of these Rana pipiens (pp. 477- 

 510) is the most common. 



Rana catesbiana, the bullfrog, is found all over the United 

 States east of the Rocky Mountains. It is the largest of the 

 family in this country, often reaching a length of six or eight 

 inches. Bullfrogs usually remain in or near water. They 

 possess a deep, bass voice like that of a bull, and when a number 

 are engaged in a nocturnal serenade they can be heard for a con- 

 siderable distance. Their food consists of worms, insects, 

 mollusks, other frogs, young water-fowl, etc. The eggs are de- 

 posited in ponds from the last of May until July. The tadpoles 

 do not become frogs the first year as do those of the leopard- 

 frog, but transform during the second or even the third year. 

 Bullfrogs are worth from one to four dollars per dozen in the 

 market, because of the demand for frogs' legs. 



Rana clamitans, the green frog, is common in the ponds of 

 eastern North America. It is little more than half as long as the 

 bullfrog, from which it may be distinguished by the presence of 

 two glandular folds of skin along the sides of the back. 



Rana sylvatica, the eastern wood-frog, is not restricted to 

 the vicinity of water, but usually lives in damp woods. It is 

 found throughout the northeastern United States. 



