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Show 1899.] THE MICE OF ST. KILDA. 81 on the two Mice from St. Kilda I can have no doubt whatever; but as to whether they are fit subjects for a binomial or for a trinomial treatment I am less certain, until I have had time to study the musculus- or sylvaticus-like Mice of the whole Palae-arctic Region. For many reasons it would seem convenient to apply the trinomial system to all forms which can be clearly shown to be local developments of any other form. By such a method a clue is given to the relationships of the various local forms-a matter of no small importance to the student of a large and difficult genus like that of Mus. On the other hand, we have in the present instance two forms which, although obviously coming within the above definition, are perfectly isolated, and do net, so far as we know, intergrade with the parent form. Regarded from this point of view, they have as much claim to be accorded full specific rank as any other island species, and the latter is, perhaps, the most satisfactory method whereby to deal with them. The following are the names which I propose :- Mus HLRTENSIS, sp. nov. (Plate IX. fig. 1.) Closely allied to Mus hebridensis, from which, however, it differs in its slightly larger size, as stated above, and also in the greater amount of buff or yellowish-brown coloration on the underside. Like Mus hebridensis, it differs from typical sylvaticus in the more uniform coloration of the upper surface of the body, in the absence of the clearly defined white underside, and in the longer feet and smaller ears. The skull is similar to that of Mus hebridensis, but appears to be larger, equalling in size that of the largest specimen of Mus fiavicollis. ' The type is No. 94.7.16.1 (British Museum coll.), the young male first collected by Mr. J. Steele Elliott. Mus MURALIS, sp. nov. (Plate IX. fig. 2.) In shape and proportions allied to Mus musculus, but more robust and larger in size. In general colour of the upper surface resembles a dark specimen of Mus sylvaticus typicus, the base of the hairs being of the same colour as in that species, but having the extremities of the majority of a sepia-brown colour; mixed among these are a certain proportion of rufous-tipped hairs, which give the animal a grizzled appearance. The colour of the under surface is very remarkable, being buff, clearly separated by a well-marked line of demarcation from the colour of the upper surface of the body. The skull, as compared with that of typical Mus musculus, is remarkable for the greatly exaggerated narrowness of the posterior opening of the nostrils. The type is No. 534 of m y own collection : it is an adult female procured for m e in 1898 by Mr. Henry Evans. P R O C . ZOOL. Soc-1899, No. VI. 6 |
