1900.] MUS SYLVATICUS AND ITS ALLIES. 395 



and Barra (if. s. hebridensis) and St. Kilda (if. s. hirtensis), where 

 it is accompanied by a very interesting shortening of the ear and 

 lengthening of the foot proportionately to the length of the body. 

 A representative of the large form occurs also in the Shetlands ; 

 but my series is not sufficiently good to enable me to decide finally as 

 to its affinities. The Iberian Peninsula and Morocco seem to be 

 the habitat of a large dull-coloured form, with regard to the exact 

 appearance and relationship of which, in default of more numerous 

 specimens, I am a little uncertain, and for the present can merely 

 allude to it under the name Mus iiayi Waterhouse. 



To turn to the smaller subspecies (if. s. intermedins), this is 

 found mainly in the British Islands and in the neighbouring 

 continental areas of Holland, Belgium, and North-west .France ; 

 but the exact limits of its distribution are as yet uncertain, and 

 it probably intergrades in all directions with other subspecies. 

 It is extremely interesting to find that specimens from such 

 clamp western localities as Lewis and Skye in the Scotch Islands, 

 Galvvay and Kerry in Ireland, and Oporto in Portugal indicate 

 that in such situations the reduction of size and darkening of the 

 colour of the upper surface reaches its maximum. It is not less 

 interesting to find some evidence that there may be two ways of 

 attaining to that greater dullness of coloration which seems to be 

 fitted to a sojourn in the moderately warm, damp regions of 

 Western Europe ; and that, whereas in if. s. hebridensis and 

 M, s. hirtensis this object is attained by rendering more uniform, 

 although not darker, the colour of the upper surface, by the en- 

 largement of the breast-band, the partial obliteration of the line 

 of demarcation between the two surfaces of the body, and the 

 extension of the yellow colour to the belly, the whole consistent 

 with a retention of large size, in M. s. celticus the same result 

 is brought about by an increase of the black-tipped hairs on the 

 back, while the belly, although retaining its pure whiteness, is 

 made less conspicuous by reduction of the size of the animal. 

 The occurrence of representatives of each of these forms almost 

 side by side on the small island of Lewis is perplexing ; but 

 Mr. de Winton informs me that the larger M. s. hebridensis keeps 

 severely to itself on the western side of the island, and .that he 

 believes that the presence of the smaller form may here be due to 

 accidental introduction. 



As regards the remaining form3, such as if. s. islandicus, arianus, 

 pallipes, griseus, chevrieri, draco, and if argenteus, little is known 

 and little can be said ; but there is evidence to show that the 

 representatives of M. sylvaticus are characterized in the north 

 (according to Badde) by larger, and in the south by smaller size, 

 and in the latter case by a proportionately smaller hind foot. The 

 thick fur and light upperside of M. s. pallipes seem to indicate 

 a development to suit great cold, combined perhaps with desert- 

 or steppe-like conditions ; but the curious differences between 

 the manner in which the young grow up in extremes, such as 

 M. s. draco and if. s. intermedins, are at present *inexplicable. 



