1899] ALLEGED NEW MICE 387 



Alleged New Mice. 



The length of the head and body of the largest St. Kilda specimen 

 of Mus hirtensis n. sp. is 1 7 mm. for the male and 110 mm. for the 

 female. This is exactly the size of a full-grown Mus sylvaticus in 

 Elginshire. The skull of an Elginshire specimen just measured 

 (apparently not an old one if we judge from the teeth) is 28 mm. 

 long, 1 mm. less than the largest St. Kilda skull. The differences in 

 ears and tail do not impress us, and still less those of colour. Even 

 in one county Mus sylvaticus shows considerable diversity of coloration. 

 At this season, when they sometimes come indoors to supplant the 

 house-mouse for a time, specimens are trapped without a speck of 

 yellow or brown on the side of neck or belly, while others are of a 

 nearly uniform reddish colour on their upper parts with a very distinct 

 line of demarcation between the white belly and sides. These are 

 minor differences, giving no evidence of more than " individual 

 variation." It may be, indeed, that they are merely " individual 

 modifications " sensu strict 0. 



Tn Texan cornfields Mus musculus sometimes assumes in summer 

 the reddish colour of some native species of Muridae, while the belly 

 often becomes white or nearly white ; the same species caught in 

 Elginshire in October sometimes has the belly almost of the same 

 colour as the back. It seems impossible to regard these as even 

 varieties. 



To illustrate further. A collection was made of an American 

 species of Cricctus (Hespcromys), and the individuals were kept in 

 captivity for a year or two. They varied in size, but did not vary 

 much in colour, which was predominantly brownish grey. A fresh 

 capture, however, was reddish, and suggested for the moment — we are 

 all open to the temptation — a new variety. After some months of 

 captivity it changed to the normal colour of the species. In all prob- 

 ability the original difference was simply the result of " modification." 



It would be interesting to trap in Sutherland and Skye to see 

 whether individuals of the Mus hirtensis type are not to he found 

 there, for it is possible that the alleged new species is not the out- 

 come of prolonged isolation, but was imported in hay or straw for 

 the minister's horse a century ago. 



The other form Mus muralis n. sp. is interesting on account of its 

 colour, but as to its skull characters it appears to us that they will be 

 found in perhaps every tenth old specimen of Mus musculus that comes 

 to hand. 



Our point, however, is apart from these details. It is that when 

 we are dealing with forms for whose characters it would be easy to 

 formulate variation-curves, this should not be neglected by those who 

 would substantiate their claim to add new species to the British fauna. 



