512 MURID^— APODEMUS 



male (B.M., No. 98.2.1. i8) from Holland, taken in September by Thomas, 

 is moulting from the rufous to a duller coat, and has just a patch 

 of the former colour on the rump, the rest of the body being dull 

 (Barrett-Hamilton, op. at., 399). 



Young: — The young are duller and more like House Mice in 

 appearance than are the adults; their upper parts have usually a 

 leaden tinge, their bellies are more slaty, and there is no well-marked 

 line of demarcation. 



Local variation : — From the evidence afforded by the skulls, 

 discussed below, it is not at all unlikely that tangible local differences 

 of colour exist among the British Field Mice ; but a very carefully 

 collected set of summer and winter specimens from several selected 

 localities must be obtained before any attempt at defining such differ- 

 ences can succeed. It was noted that amongst British specimens 

 summer skins from Oxfordshire and Leicestershire were the brightest 

 and reddest; an old nursing female from Glamorganshire, taken in 

 July, was, however, as brightly coloured as any of them. Field Mice 

 from the London Parks are very dark and smoky, as are the birds and 

 Lepidoptera, but in their case the change is doubtless a pathological one. 

 The sub-species Mus s. celticus, Barrett-Hamilton {op. cit, 401), was based 

 upon some small dark-coloured specimens from Co. Kerry, Ireland, and 

 similar specimens from this locality were described long ago by Jenyns 

 {Ann. and Mag. Nat. Hist., 1841, June, 268) ; the typical series, however, 

 are all immature, and do not differ from young individuals of A. s. 

 sylvaticiis. In a long series taken in Skye by Mr P. D. Montague in 

 March, and by Mr C. H. B. Grant in July (see note on p. 422 above), 

 the backs are rather dark and the ventral surfaces frequently show 

 traces of a median wash of yellow. Specimens from the Highlands also 

 appear to average darker than those from southern England. These 

 Scotch mice make an approach towards the small dark form inhabiting 

 Bute, which, having distinctive skull characters in addition, is described 

 below as a distinct sub-species. 



The skull (Fig. 89) is lightly built, and of moderate size; its dorsal 

 line is at first straight, rising from the nasal tips to the inter-orbital 

 region, whence it is gently convex to the occiput, the highest point being 

 in the mid-parietal region ; its ventral line is nearly horizontal to behind 

 the tooth-rows, and then slopes rapidly down to the level of the lower 

 surfaces of the bullae. The brain-case is very smooth, of oval or sub- 

 circular form ; the upper limits of the temporal fossae are marked on 

 its sides and shoulders by a very feeble ridge, which on each side is 

 continued forwards into the smoothly squared edge of the hinder part 

 of the inter- orbital region. The inter-parietal is short, but very wide; 

 its lateral extremities are drawn out as pointed processes which approach 

 the squamosals, and it is wholly posterior to the straight lambdoid 



