NOTES ON THE MICE OF ST KILDA 127 



greater dimensions than has previously been supposed, speci- 

 mens over 120 millimetres in length of head and body being 

 not uncommon, while some attain as much as 129, and it is 

 quite possible that larger examples may yet be obtained. 

 The varying colour of the under surface is interesting, for 

 it affords an intermediate form between the white-bellied 

 Apodemus sylvaticus of the mainland and the rufous-bellied 

 A. hebridensis of the intervening Outer Hebridean islands. 

 It is difficult to understand on what grounds these two mice 

 have been given full specific rank by Miller in his recent 

 great work on the Mammals of Western Europe. 



As data hitherto published on the measurements of this 

 species are of a meagre description, it is desirable to pub- 

 lish the following details relating to the mature specimens 

 obtained during these visits to St Kilda, most of which I 

 have presented to the collections in the Royal Scottish 

 Museum. The dimensions are in millimetres; and only 

 specimens having the Head and Body measurement 100 

 millimetres or more are included in the tabulation on p. 126. 



MUS MURALIS. 



AIus muralis, Barrett-Hamilton, P.Z.S., 1899, p. 81. 

 Mus musculus muralis, Trouessart, Faune mamm. iV Europe, p. 146 

 (1910). 



This is the house mouse of St Kilda, and being such is 

 not found out of Hirta the only inhabited isle of the group. 

 On this island, however, it is not confined to the houses, 

 where it is very abundant, but occurs in the crofts, finding 

 shelter in the walls and cleits. Forty specimens were pre- 

 pared, chiefly females, one of them being pregnant and 

 containing nine foetuses. A number of young were also 

 trapped. Here again some of the examples in the collection 

 greatly exceed in their measurements previous records. I 

 did not obtain any specimens in which the under surface 

 was smoky, and am very doubtful if such occur. In 

 general colour the upper surface of all the adults 

 resembles that of a rather light-coloured example of the 

 ordinary House Mouse ; but the coloration of the under 

 surface presents a remarkable departure from that species, 



