THE BROWN OR COMMON RAT 613 
from silver to a light yellowish-brown. Except under the chin, where 
the hairs are white throughout, all the hairs have slaty or dusky bases. 
The ears are of a dull hair-brown. The hands and feet are greyish 
flesh-coloured (not pink as in vattws). The tail is inconspicuously bi- 
coloured, being a dull dark brown above and yellowish-white below; 
the fine hairs, which clothe it but do not conceal the skin, are blackish 
above, whitish below. 
Barrett-Hamilton observed the moult in a specimen of “ Azbernzcus” 
taken at Kilmanock on 3rd August 1912. There is probably also a 
spring moult; O. Jones (A Gamekeeper's Notebook, 26) says the coat 
is rusty red then, especially if the rats are living in burrows in soil, and 
if short of food or living on carrion, which delays the moult. It is 
probable that all murines have distinct summer and winter coats. 
The pelage of the young (soon after they have left their dam) does 
not differ conspicuously from that of the adults: it is rather softer, 
fuller, and duller in colour. The young are slenderly built; their ears 
relatively thin and, together with the tail and feet, relatively longer than 
in the adults. On cursory examination they may easily be confused 
with vazttus, but all may be correctly determined by comparing their 
proportions with those of vattws of similar age, apart from the quality 
of the fur and the characters of the skull. 
Local variation :—William Thompson’s (Proc. Zool. Soc., 1837, 
52) description of the Irish Rat, A/us hzbernicus, has given rise to a 
bulky literature. It was supposed to be characterised by the possession 
of white fore-limbs and of a white breast spot, but these have since 
proved to be very variable characters, more frequently absent than 
present, the chest spot when present being of various and often 
asymmetrical shapes. Apart from these features, Azbernicus differs 
from ordinary brown specimens in the uniform dusky hue of the 
complete pelage and the absence of a white underside; and it is, in 
this respect, parallel to melanisms of the rabbit. The skin also is 
dusky, and a peculiarity is the frequent presence of numerous grey 
hairs on the flanks, which give a very blue appearance. 
No doubt owing to its black colour, it was compared by Thompson 
with Z. vrattus, and in Bell’s 2nd edition it is mentioned by Tomes in 
the article on that species. Others (as Southwell, Zoo/ogzst, 1889, 321, 
and Tvans. Norf. and Norw. N. H. Soc., ii., 419) have thought it a 
hybrid. While fully cognisant of these errors, Eagle Clarke (in Harvie- 
Brown and Buckley’s Vert. Fauna of the Outer Hebrides, 1888, 362) 
was at first led to regard it as a distinct species, but later (Zoologzst, 
1891, 1) he joined Barrett-Hamilton in describing it as an interesting 
melanism of £. norvegicus, an opinion already expressed by Blasius 
in 1857, and by de I’Isle in 1865 (of. cet, 189). The latter used 
hibernicus, together with the melanistic races of House Mice, in 
