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Show 84 MR. G. E. H. BARRETT-HAMILTON ON [1^°- ?' since the whole of our British Mammalian fauna is so similar to that of the Continent that it is inconceivable (unless all the species are introductions) that it can have existed in our islands for any, geologically speaking, long period of time. Even the most plastic of British Mammals, such as the Squirrel \ have only advanced a comparatively short distance on the road of differentiation ; and as regards Birds there is a precisely similar story to be told, there being only one really well-differentiated peculiar British species, the Red O+rouse, Lagopus scoticus (Lath.). In fact, one of the strongest arguments against m y friend2 Dr. R. F. Scharff's brilliant theories as to the antiquity of the Irish fauna (which is presumably older than that of Great Britain) is that, were it so old as he would make it, we should expect to find not only peculiar species but even peculiar genera among the mammals of Ireland, whereas a most careful study has hitherto only sufficed to distinguish one certainly peculiar species, the Irish Stoat, Putorius hibernicus Thorn. & H.-B., and that bears in itself very clear evidence of its recent origin. Another species or subspecies, the Irish Hare, Lepus hibernicus Bell, seems also to be distinguishable, but it is not nearly so distinct as the Stoat. Among Birds, Reptiles, and Amphibians naturalists have hitherto failed to find any peculiar local forms, although it is evident that the Grouse of Western Great Britain and of Ireland is folio wing the same route as the Irish Stoat and Hare. Can there, then, be any great difficulty in supposing that Mus hirtensis is indigenous to St. Kilda, and that it reached the island at a comparatively recent geological period, when a land-surface existed connecting the Shetlands, Orkneys, Scotland, the Hebrides, St. Kilda, and Ireland, and that this connection must have been so recent geologically that few of our native mammals have had time to develop into species or even subspecies distinct from those of the Continent of Europe ? That the Mouse of St. Kilda should be the one in which variation has proceeded farther than in other localities is quite in accordance with the isolated situation of and confined space on the rock, together with its full exposure to the Atlantic winds; and w e have an apparently parallel instance in the case of the W r e n of the island, Troglodytes hirtensis Seebohm, and perhaps also in the possible existence of a race of small dark-coloured Field-Mice3 in the West of Ireland. To assert that the Mouse of Iceland has reached that island along a formerly continuous land-area would be a Aery different matter, since not only is there a deep channel between the Faroes and Iceland, and even between the former islands and the Shetlands, but if we consider that Mus islandicus is native to Iceland, then we should expect to find a similar or representative species in the Faroes, and of that w e have as yet no record. Yet that there has never been such a land-connection will not, 1 Sciurus Icucourus Kerr. 23 SSeeee JPernoyc.ns E,, AIn. nA.c a&d .M,a Jgu.l y' N1a8t.9 7H,i spt.. 4 v2o7l.. vii. p. 268 (1841). |