244 



Mr. G. A. Boulensjer on the Races and 



to individuals ; this is well shown by two specimens from 

 Florence, representing the two extremes. A more or less 

 distinct process between the two horns is sometimes present, 

 as in a specimen of the var. lessonce from Noville, Switzer- 

 land **. 



Fig. 2. 



Showing the shape of the tongue in specimens from Berlin, var. ridi- 

 bunda (a, b), Florence, f. typica (c, d), and Noville, var. lessonce (e). 



The Head. 



According to Bolkay j", the three forms distinguished by 

 him as species differ in the following points : — 



R. esculenta. Head comparatively narrow, tip of snout 

 ending in a blunt point ; interorbital space equal to half, or 

 frequently to three-quarters, the breadth of the upper eyelid. 



R. ridibunda. Head broad, short, tip of snout bluntly 

 rounded ; interorbital space equal to one-third the breadth of 

 the upper eyelid. 



R. chinensis. Head narrow, long, and very pointed at the 

 end ; interorbital space equal to half the breadth of the upper 

 eyelid. 



There is no constant difference in the shape of the head 

 between the two first, and although it is a fact that R. chi- 

 nensis usually has a narrower head and a more pointed snout, 



* This process is usually distinct in the Indian R. hexadactyla, Less. 

 It has been regarded as a specific character in a Central American frog 

 (JR. trilobuta, JMocquard), which may be merely a young JR. halecina, L. 



f Proc. Washingt. Ac. Sc. xiii. 1011, p. 75. 



