SPECIES OF ARVICOLA. 
429 
never come near houses, and do no injury to the crops. 
In all the places where I have seen them, the common 
water rat was unknown ; nor have I ever observed any 
other than a very slight variation in the tint of the black 
fur. Although pretty numerous in many places, they no 
where swarm like the common or the black rat. 
The general description of the Common Water Rat is 
almost the same as the above. In the latter, however, the 
fur is light brown with some dark hairs, much shorter and 
less close ; the external ears are much more covered with 
hairs, and less concealed by the fur ; and the tail is a little 
compressed towards the end. The size is also larger. 
Another difference, which by many would be considered 
more important, exists in the number of the caudal verte- 
bras ; but, unfortunately, my notes on this subject do not 
apply to a sufficient number of individuals. 
When I have completed my observations on these species^ 
I shall give a more detailed description of the present, to- 
gether with a full account of the other ; respecting which 
there are many inaccuracies in our books, some authors 
saying that its feet are webbed, which is not^tiie case, that 
it swims with difficulty, which is not true, and that it feeds 
on fishes, which appears more than doubtful. In the mean 
time the two species may be characterized as follows. 
Arvicola amphihius. Brown Water Rat. — Fur pale red- 
dish-brown, mixed with dark brown hairs above, light grey 
beneath ; tail short, round, slightly compressed towards the 
end. 
Arvicola ater. Black Water Rat. — Fur black, dark blu- 
ish-grey beneath ; tail short, round in its whole length. 
The naturalists of Aberdeen have abundant opportunities 
of completing the description of this animal, it being plenti- 
ful along the banks of a stream which washes the garden 
wall of the University of King''s College. 
