512 MURIDAE—APODEMUS 
male (B.M., No. 98.2.1.18) 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, of. czt., 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 AZus s. celticus, Barrett- Hamilton (of. czt., 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 fram young individuals of A. s. 
sylvaticus. Ina 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 bulla. The brain-case is very smooth, of oval or sub- 
circular form; the upper limits of the temporal fosse 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 
