640 MURIDA—MUS 
land mice; they are said to be very numerous among the crofts, but 
after the corn is cut they betake themselves to the houses. 
The House Mice from Braescleit and Barvas, western Lewis, differ 
in no way from ordinary musculus (W. Eagle Clarke, Ann. Scott. Nat. 
FHitst., 1908, 198; Hinton and Hony, Zhe Scottish Naturalist, 1916, 221). 
From fields at the Butt, or northern extremity, of Lewis, Eagle Clarke, 
however, obtained specimens which approach murals in their large 
size, but do not differ from szzscudus in coloration or in skull structure. 
On North Uist ordinary House Mice, and others which are practically 
identical with sawral’s in size and colour, though slightly paler below, 
occur quite commonly in the houses at Lochmaddy. Intermediates 
between the two forms have not been observed, and although the only 
but imperfect skull seen seems to agree better in form with that of 
musculus than with that of mralzs, it is not impossible that the variety 
may be a second form of the latter species (Eagle Clarke, of. czz.). 
A youngish female from Islay has the whole ventral surface of a 
beautiful clear white, separated by sharp lines of demarcation from 
the flanks, which are but slightly lighter than the back, the general dorsal 
colour approaching that of Apodemus (Hinton, Ann. Mag. Nat. Hist., 
July 1914, 130, and June 1915, 583). Specimens from Skye, and a male 
from Tiree (Proc. Zool. Soc., 1913, 835) trapped in sand-hills, represent 
the yellowish outdoor form, while one obtained by Mr Kinnear in 
Barra, from a hole in a field, is of normal indoor appearance. 
Specimens obtained for Ogilvie-Grant from Hermaness Hill, North 
Unst, Shetland, in the autumn of 1914, are remarkable merely for 
their relatively stout tails. 
Exceptional variation :—Quite apart from the well-known differ- 
ences in pattern and colour presented by the tame “fancy” breeds, the 
House Mouse shows many individual or family variations, particularly in 
its coloration and pelage. Such variations have formed the bases of most 
of the specific or sub-specific names enumerated in the synonymy above. 
True albinos, wholly white or cream-coloured with pink eyes, 
partial albinos, white specimens with dark spots, dark specimens with 
light spots, and melanistic examples, are not rare. Fatio’s JV. poschiavinus 
was based, with much hesitation, on a Swiss melanic race. 
Tomes (in Bell, ed. ii, 296) describes a great number “killed in 
a wheat-rick at Welford-on-Avon, which were of a light grey colour, 
without the least mixture of brown,” and Collett (165) speaks of a 
similar variety in Norway. In another rick at Welford Hill, Tomes 
found all the mice to be “of an unusually dark colour, especially along 
the dorsal line, which was nearly black”; this latter form is apparently 
that to which the names “Rick Mouse” and “Barn Mouse” are 
applied (Tomes, of. czt., 300), and which occasionally, though not 
always, attains an unusually large size. 
