AMERICAN FROGS OF THE GENUS RANA. 417 



II. Toes ending in very small discs; outer metatarsals separated 

 nearly to the base; interorbital space equal to or a little less 

 the width of upper eyelid; nasal bones widely separated from 

 each other. 



A. Loreal region moderately oblique; toes entirely webbed or two 

 phalanges of fourth free. 



1. Tips of fingers swollen; vomerine teeth behind level of 

 choanse; tympanum f to f diameter of eye; tibio-tarsal articu- 

 lation reaching tip of snout or beyond; head broader than long. 



No dorso-lateral fold; tympanum distinct; heels not overlapping; 

 tibia If to 2 times in length from snout to vent; no outer metatarsal 



tubercle; male without vocal sacs R. tarahumarae, Blgr. 



Dorso-lateral fold, if distinct, very broad and flat and restricted to 

 the anterior half of the body; tympanum feebly distinct, ill-defined; 

 heels overlapping; tibia if to If times in length from snout to vent; 

 an outer metatarsal tubercle; male with internal vocal sacs. 



R. hoylii, Baird. 

 A moderately prominent dorso-lateral fold, extending to the hip, 

 its distance from its fellow, on the back, 3| times in length from snout 

 to vent; tympanum very distinct; heels overlapping; tibia If times 

 in length from snout to vent; no outer metatarsal tubercle. 



R. piistulosa, Blgr. 



2. Tips of fingers obtuse or rather pointed; vomerine teeth 

 between choanse; tympanum | to f diameter of eye; tibio- 

 tarsal articulation reaching eye or tip of snout; tibia If to 

 2t times in length from snout to vent; dorso-lateral fold 

 prominent, its distance from its fellow, on the back, 4 to 5§ 

 times in length from snout to vent; no outer metatarsal tu- 

 bercle; head as long as broad or a little broader than long; 

 male with internal vocal sacs R. palmipes, Spix. 



B. Loreal region vertical or nearly so; toes f to f webbed; tips of 

 fingers swollen; tympanum ^ to f diameter of eye ; tibio-tarsal 

 articulation reaching eye or between eye and tip of snout; heels 

 overlapping; tibia 5 to 6 times as long as broad, If to 2 times 

 in length from snout to vent; dorso-lateral fold prominent, 

 its distance from its fellow, on the back, 5 to 6 times in length 

 from snout to vent; no outer metatarsal tubercle; head as 

 long as broad or a little longer than broad; male without 

 vocal sacs R- coeruleopunctata, Stdr. 



The American frogs all belong to the subgenus Rana, agreeing with 

 the type-species, R. temporaria, L., in the structure of the pectoral 



