AMPHIBIANS 169 



food of frogs is insects, worms and snails. Frogs have a considerable 

 economic importance in consequence of the demand for the hind legs for 

 food, large quantities of which appear in the fish markets of the large 

 cities. 



Key to the United States Species of Rana 



ai In the States east of the Sierra Nevadas. 

 bi Dorso-lateral ridges present (Fig. 95). 



Ci With conspicuous rounded, elongate or squarish spots 

 between the dorso-lateral ridges, 

 di Skin smooth, with usually 2 rows of spots between the 

 dorso-lateral folds, 

 ei Spots rounded or elongate; color tone of body 



green R. pipiens. 



e-i Spots squarish; color tone of body brown R. palustris. 



d2 Skin warty; numerous spots on the back and sides. 



ei Total length three times the length of head R. areolata. 



eo Total length two and a half times the length of 



head R. ccsopiis. 



C2 Without large spots on the back. 



di Large aquatic frogs; head green R. damitans. 



d.2 Small wood-frogs; head brown. 



ei Length of leg to the heel exceeds total length of 



body R. syhatica. 



e2 Length of leg to the heel less than or equal to total 



length of body R. cantabrigensis. 



bz Dorso-lateral ridges absent. 



Ci Very large frogs, upwards of 200 mm. long R. catesbeiana. 



C2 Smaller, medium sized frogs, under 100 mm. long, 

 di In the northern and eastern States. 



ei Back mottled R. septentrionalis. 



t2 Back plain, not mottled R. virgatipes. 



di In the Gulf States R. gryilo. 



a2 On the Pacific slope and in the Rocky Mountain region, 

 bi Dorsolateral ridges distinct the full length of the body. 

 Ci A dark cheek patch present. 



di Cheek patch brown; white stripe from the snout to 



the shoulder R. pretiosa. 



d2 Cheek patch black; white stripe from the eye to the 



shoulder R. aurora. 



C2 No dark cheek patch R. onca 



hi Dorsolateral ridges absent or indistinct or broken R. boylii. 



R. pipiens Schreher. Leopard frog (Fig. 93). Body green, gray or 

 brown above with light-colored dorso-lateral ridges, between which are 

 I to 3 irregular rows of elongate or rounded dark spots, each edged with 

 yellow or white; similar spots on the flanks and legs; belly white; length 



