84 MR. G. E. 11. BARKETT-HAMILTON OK [I'eb. 7, 



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 introductious) that it can have existed in our islands 

 for anj^, 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 differen- 

 tiation ; and as regards Birds there is a precisely similar story to 

 be told, there being only one really well-differeutiated peculiar 

 British species, the Red Grouse, Lagojms scoticus (Lath.). lu 

 fact, one of the strongest arguments against my friend ^ 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 liihernicus 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 pecuHar local forms, although it is evident that the Grouse of 

 Western Great Britain and of Ireland is folio wiug the same route 

 as the Irish Stoat and Hare. 



Can there, then, be any great difficulty in supposing that Mus 

 liirtensis 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 Avith its 

 full exposure to the Atlantic winds ; and we have an apparently 

 parallel instance in the case of the Wren of the island, Troc/lodytes 

 liirtensis Seebohm, and perhaps also in the possible existence of a 

 race of small dark-coloured Eield-Mice ^ in the West of Ireland. 



To assert that the Mouse oi: Iceland has reached that island 

 along a formerly continuous land-area M^ould 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 we have as yet no record. 



Yet that there has never been such a land-connection will not, 



^ Sciums leucourus Kerr. 



2 See Proc. E. I. Acad., July 1897, p. 427. 



3 See Jenjns, Ann. & Mag. Nat. Hist. toI. vii. p. 268 (1841). 



