ON TWO RECENTLY DESCRIBED MICE FROM ST. KILDA 131 



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 a gradual one. As regards the 

 specimens obtained 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. We find thus 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 point 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 under side. 



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 preserved in spirit. These Mice are, if possible, of 

 even greater interest than the Mus sylvctticus-\\ko. species, since they 

 are characterised by the possession of a buff-coloured under side 

 clearly marked off from the colour of the upper side by a distinct 

 line of demarcation, and are thus very different from the ordinary 

 almost uniformly smoky-brown coloured House Mice with which 

 every one is familiar. The upper surface is also not of the typical 



