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Show 242 MR. G. A. BOULENGER O N RANA ARVALIS. [Apr. 20, 6. Remarks on Specimens of Rana arvalis exhibited in the Society's Menagerie. By G. A. BOULENGER, 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. M y 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 Smith1. 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 R. 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 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 m y monograph of the Ranee 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 choanae, and would as regards this character fall in the section R. temporaria?! 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. |