AMERICAN FROGS OF THE GENUS RANA. 415 



second; tibia-tarsal articulation reaching tympanum or eye; heels 

 meeting or narrowly separated; tibia 2\ to 2| times in length from 

 snout to vent; web extending to tip of fourth toe; no dorso-lateral 



fold R. grylio, Stejn. 



Vomerine teeth on a level with posterior borders of choanje, or just 

 behind them; first and second fingers equal; tibio-tarsal articulation 

 reaching eye; heels meeting or slightly overlapping; tibia 2 to 2^ 

 times in length from snout to vent; one or two phalanges of fourth 

 toe free; dorso-lateral fold present or absent . . .R. septcntrionalts, Baird. 



2. Male with internal vocal sacs ; dorso-lateral fold usually very 

 distinct; vomerine teeth between the choanse or just behind 

 the level of their posterior borders; first finger as long as or a 

 little longer than second; tibio-tarsal articulation reaching 

 tympanum, eye, or between eye and tip of snout; heels meet- 

 ing or overlapping; tibia 3 to 4 times as long as broad, If to 2| 

 times in length from snout to vent; one or two phalanges of 

 fourth toe free. 



Dorso-lateral fold not extending beyond the sacral region. 



R. clamitans, Daud. 

 Dorso-lateral fold extendmg beyond the sacral region. R. onca. Cope. 



3. Male with external vocal sacs; tympanum not larger than 

 eye; first finger as long as or slightly longer or shorter than 

 second; heels meeting or not. 



Head as long as broad; tibio-tarsal articulation reaching shoulder or 

 tympanum; tibia 2f to 2f times in length from snout to vent; two 

 phalanges of fourth toe free; no dorso-lateral fold . . R. virgatipcs, Cope. 

 Head broader than long; tibio-tarsal articulation reaching tympanum 

 or eye; tibia 2 to 2| times in length from snout to vent; fourth toe 

 webbed to the tip, or last phalanx free; usually a more or less dis- 

 tinct dorso-lateral fold R. montczumce, Baird. 



B. Glandular dorso-lateral fold very distinct, extending to the hip 

 (exceptionally interrupted posteriorly); nasal bones widely 

 separated from each other. 

 1 . Outer metatarsals separated nearly to the base ; toes obtusely 

 pointed, f to nearly entirely webbed; tibio-tarsal articulation 

 reaching eye, tip of snout, or a little beyond; tibia 3| to 5| 

 times as long as broad, If to 2to times in length from snout to 

 vent. 



a. Male with vocal sacs. 

 Head as long as broad or a little broader or a little longer; interorbital 

 space much narrower than upper eyelid ; dorso-lateral folds narrow or 



