838 MAJOR G. E. H. BARRETT-HAMILTON AND 



Mus MuscuLus Liniifeus. 



One, TiREE. 



jS^o. 147, male, 10 July 1912. 



An example in the j^ellowish outdoor pelage. It was trapped 

 in sand-hills. 



In conclusion we have to sum up the distributional evidence 

 and offer a few remarks, of a quite tentative character, upon 

 its meaning as it appeals to us at present. Of the shrews, 

 iS. minutus occurs throughout the Outer and Inner Hebrides, 

 and in the Orkneys, Ireland, and other islands ; S. araneus, 

 on the other hand, is conlSned to the mainland, the Inner 

 Hebrides and such islands as Anglesea and Wight ; it is 

 represented in Islay by the peculiar S. grantii connected 

 morphologically and geographically with the parent form by 

 means of the partially differentiated Jura form. We may 

 therefore perhaps conclude that S. mimdus was the first form to 

 ariive in this region ; but this point is of little importance, 

 because both species have had representatives in Britain from an 

 extremely early period, and the problem before them in the past 

 may have simply resolved itself into a contest of endurance to 

 decide which of them could survive the rigours of the glacial 

 period in the outlying districts. Be this as it may, one fact 

 stands out clearly, that Isla}^ has been separated from the 

 mainland longer than have the other islands of the Inner 

 Hebrides, with Jura approaching it in age. The microtine 

 species lead us to much more definite conclusions. We have in 

 the Inner Hebrides two genei-a, Microtus and Evotomys ; the 

 former alone, so far as is known, inhabits the Outer Hebrides as 

 well. As is well known, neither genus occurs in Ireland, and 

 Microtus alone is met with in the Orkneys. There is a great 

 •difference, however, between the Orcadian and the Hebridean 

 species of Microtus : the Orcadian forms are members of the 

 M. arvalis group, while those of the Hebrides are members of 

 the M. agrestis group. jSTow, at first sight, having regard to the 

 fact that M. orcadensis and 31. sandayensis have a near ally in 

 the Guei-nsey M. sarnius and another in the late pleistocene 

 English M. corneri, as well as to the fact that this group is no 

 longer represented on the mainland of Biitain, one might feel 

 inclined to look upon the Orcadian fauna as an older one than 

 that of the Hebrides. On the other hand, we have to remember 

 that both the M. agrestis group and the genus Evotomys appeared 

 in Britain long before any of the other modern groups of Yoles. 

 Each is represented in such an early horizon as that marked by 

 the Grays brickearth by a form much like the living ones ; while 



