242 MR. G. A. BOULENGER ON RANA ARVALIS. [Apt. 20, 



6. Remarks on Specimens of Rana arvalis exhibited in the 

 Society^s Menagerie. By G. A. Boulenger, F.Z.S. 



[Eeceiyecl April 14, 1886.] 



(Plate XXIV.) 



An interesting addition has recently been made to the series 

 of Batracliians in the Society's menagerie— the Osyrrhine Frog, 

 Rana arvalis, Nilsson, so often described and its specific validity 

 discussed. It is, with the exception of Rana iberica, Blgr., the 

 only European Batrachian as yet never figured. The accompanying 

 illustration (Plate XXIV.) is intended to supply this desideratum. 

 My friend Professor Born, of Breslau, favoured me this spring 

 with about 50 breeding specimens of the Frog in question, some 

 of which have been presented to the Society. Two years ago, I 

 also received a number of these Frogs from the same gentleman, 

 which have afforded me an opportunity of verifying the additional 

 observations on the characters of the species recently made by 

 Pfliiger and Smith'. These authors have shown that some of the 

 characters hitherto regarded as diagnostic comparatively to R. tem- 

 jJoraria are not constant. Thus the shape of the snout, often 

 given as the principal distinctive character of the two species, is 

 not absolutely constant ; and specimens of R. arvalis may be found 

 with the snout less pointed than certain specimens of R. temporaria. 

 i^lso breeding males of the former species possess black rugosities 

 on the thumb in every respect similar to those of R. temporaria. 

 This statement I have been able to verify not only on the Breslau 

 specimens, but on a Swedish one, for which I am indebted to Dr. 

 Westerlund. However, the breeding specimens from Copenhagen, 

 in M. Lataste's collection, which I described in my monograph of 

 the Ranee temporaries, have grey, not black, asperities. It is therefore 

 a question whether the colour of the copulatory asperities does not 

 vary according to localities. Besides, the web between the toes is 

 longer in the Copenhagen specimens. The character derived from 

 the vomerine dentition has also been shown by these authors to be 

 an unreliable one. I may add that the remark is not only true in this 

 case, but applies to European species of Ra?ta generally ; among the 

 hundreds of specimens of Rana esculenta which have been examined 

 by me, not a few have the vomerine teeth inserted behind the line 

 of the choanse, and would as regards this character fall in the 

 section R. temporaries ! Differences in the dentition exist which 

 may often assist in the discrimination of species, but are not 

 sufficiently constant to be regarded as good characters. The 

 criterion for the easy distinction of R. arvalis from R. temporaria 

 is the metatarsal tubercle ; this character is an infallible one, and will 

 remove any hesitation in the determination. Of greater importance 

 still, but less easily ascertainable, is the character of the spermatozoa. 

 Should any one still entertain doubts as to the specific validity of 



1 Arch. f. ges. Physiol, xxxii. 1883, p. 525. 



