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Show 1899.] THE MICE OF ST. KILDA. 79 the form of M. sylvaticus described by my friend Mr. W. E. de Winton1 from the Isle of Lewis, Outer Hebrides. The adult female from St. Kilda (which is in spirit) may possibly not be so stout in foot nor so small in ear as the Hebridean Mice, but the two forms are very close to each other, and there can be no doubt that the St. Kilda Mice belong to the Hebridean type, although their rufous belly has carried them a little further along the same line of development in which Mus hebridensis deviates from typical sylvaticus. In this respect I find that the most rufous skin of all is the first one collected by Mr. J. Steele Elliott. In it there is no perceptible line of demarcation between the colours of the upper and under surfaces, the transition from the one to the other being, as stated above, quite gradual. As regards the specimens obtained for me by Mr. Evans, the colour of the belly of the adult female, which is in spirit, agrees with that of Mr. Steele Elliott's specimen ; but in the male, which has been made into a skin, the belly is slightly lighter, the median broad buff belly-line of Mus hebridensis is more evident, and there is a just perceptible line of demarcation between the colours of the two surfaces. The colour of the upper surface of the body of all the specimens is also, as in Mus hebridensis, more evenly distributed than in typical sylvaticus, there being less tendency to the development of a dark dorsal line. It is exceedingly interesting to find this graduating series, and to have the gap between Mus sylvaticus and the St. Kilda Mouse partially bridged over by the occurrence of Mus hebridensis on the intervening islands. This slight variation of the St. Kilda specimens in regard to the colour of the belly, the white colour of which is so extremely constant in and characteristic of Mus sylvaticus, is worthy of note, being exactly what we should expect to find in a comparatively new species which has not yet finally settled down into its new groove of development. W e thus find that while in the colour of the belly some of the St. Kilda Mice may vary in the direction of Mus hebridensis, it is in this very respect that the latter form may vary in the direction of Mus sylvaticus. Indeed, in this regard Mus hebridensis is very variable, and I have examined some Isle of Lewis specimens, especially those from the eastern coast, which come very close to Mus sylvaticus in the colour of the underside. In addition to the above mice, Mr. Evans also procured for me five specimens of the House-Mouse of St. Kilda, of which the Museum already possessed five specimens collected on previous occasions and now preserved in spirit. These mice are, if possible, of even greater interest than the Mus sylvaticus-like species, since they are characterized by the possession of a buff-coloured underside clearly marked off from the colour of the upperside by a distinct line of demarcation, and are thus very different from the ordinary almost uniformly smoky-brown-coloured House-Mice 1 Zool. 1895, p. 369. |