612 MURIDA:—EPIMYS 
than is &. ra¢tus, and ina somewhat different direction. While vattus 
is essentially fitted for a free, semi-arboreal life, xorvegécus has pursued 
a more earth-bound course. It has acquired accordingly a stouter and 
heavier body, a shorter tail, and its structure, in many points, has 
suffered modifications adapting it for burrowing, swimming, and the 
other activities incidental to its peculiar mode of living. 
Description :— Though generally resembling 4. vatéus in form, the 
Common Rat is characterised by its relatively large size, great weight, 
robust form, short, thick ears, and by its shorter tail, which is never as 
long as the head and body. 
The snout is relatively blunt. The eyes are small, though some- 
what larger than in va¢tus. The ears are short, about one-third as long 
as the head and scarcely reaching the eyes when laid forward; their 
substance is thick and opaque, and they are clothed with fine short 
hairs; in young animals they are relatively large and thin. The 
hands and feet are much like those of va¢tus, although more robust ; 
the fingers and toes have similar proportions, and the number and posi- 
tions of the palmar and plantar pads are essentially the same in both 
species. The pads, especially those of the sole, are, however, relatively 
small in xorvegicus ; in the hand and foot there is sometimes a small 
free pad external to that at the base of digit 5 ; and in the foot another 
is occasionally present, to the inner side of that at the base of digit 1. 
The tail differs from that of ra¢tws in being shorter and stouter, while 
the annulations are masked to some extent by the greater distinctness 
of their component scales ; it has about one hundred and eighty rings 
in all, and a few small hairs rise from beneath each scale. The female 
has twelve mamma, arranged as two pectoral, one abdominal, and three 
inguinal pairs. 
Pelage:—The underfur is thick. The grooved bristles are much 
finer and present in much fewer number than in va¢dus, the long black 
dorsal hairs are shorter ; in consequence of these differences the fur as 
a whole is rather softer and less harsh in quality than that of ratius, 
but the greater length of the underfur imparts a rougher and shaggier 
appearance, particularly noticeable on the belly, than that of 4. vattus 
vattus. 
The whiskers are relatively. short, not extending beyond the ear 
when pressed backward; the lower ones are whitish, the remainder 
black in colour. 
In the typical form the colour is darker on the back, where the tips 
of a greater or less number of the hairs are black, and lightens towards 
the sides, where dirty yellowish or whitish hair tips predominate. The 
general tone of the upper parts is a very variable greyish-brown, lined 
with black, and with an occasional reddish tinge over the rump and 
loins. The underside is variably lighter, the colour of the belly varying 
