242 MR. G. A. BOULENGER ON RANA ARVALIS. __[Apr. 20, 
6. Remarks on Specimens of Rana arvalis exhibited in the 
Society’s Menagerie. By G. A. Boutenesr, F.Z.S. 
[Received April 14, 1886.] 
(Plate XXIV.) 
An interesting addition has recently been made to the series 
of Batrachians in the Society’s menagerie—the Oxyrrhine 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- 
poraria 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 &. arvalis may be found 
with the snout less pointed than certain specimens of R. temporaria. 
Also breeding males of the former species possess black rugosities 
on the thumb in every respect similar to those of A. 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 Rane temporaria, 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 Rana 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 choane, and would as regards this character fall in the 
section 2. temporarie! 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. 
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