MAMMALIA. : , 143 
transport the substances it preys upon, I suspected that it had cheek-pouches, 
but none were found on examination. The ermine is a most inveterate enemy 
to this species, and pursues it into the sleeping apartments. 
The Mus leucopus may be considered as the American representative of the 
European field-mouse (mus sylvaticus, Linn.), which it greatly resembles, and 
perhaps Pennant is quite right in terming it only a variety. The mus sylvaticus 
appears to have generally a more tapering, acute tail. Dr. Godman’s description 
of the Mus agrarius corresponds so exactly with our animal, that I have quoted it 
as asynonym; but the Mus agrarius of Pallas differs, in having small ears. Dr. 
Harlan mentions, that several varieties. of the mus syloaticus exist in the neigh- 
bourhood of Philadelphia; but his description, which seems to be a translation 
of Desmarest’s account of the European animal, does not agree with any variety of 
the mus leucopus that I saw to the north. The varieties that I met with differed 
principally in the size of the body, and the length of the tail. Specimens from the 
mouth of the Columbia were considerably larger than those from Hudson’s Bay. 
DESCRIPTION. 
The American Field-Mouse has a larger head than the English domestic mouse; but in its 
general form it is similar to that animal. On the other hand, its head is smaller than that 
of Wilson’s meadow-mouse; its body less fleshy, and it weighs less. Its muzzle is rather 
sharp. The whiskers are much longer than the head, part of them are black, the rest white. 
Eyes moderately large. Lars large, erect, membranous, of an elliptical form, with rounded 
tips, and covered rather thinly with short adpressed hairs. 
The fur of the body is very fine, but not long, and is throughout of a dark, bluish-gray 
colour from the roots to near the tips. The colour of the upper parts is hair-brown, darkest 
on the crown of the head, and along the back; the sides are of a lighter hue, approaching to 
yellowish-brown, or sometimes, together with the hips, to reddish-brown. The cheeks have a 
still more lively colour than the sides, being somewhat rufous. The upper lip, a space on 
each side of the mouth, the chin, all the under parts, the inside of the thighs, and the whole 
of the legs and feet, are white. 
The tail is thickly clothed with short hairs lying pretty smoothly, no scales whatever being 
visible. Its upper surface is of a hair-brown colour, considerably darker than any other part 
of the animal, and contrasts strongly with the inferior surface, which is white; the line of 
contact of the two colours is straight and well defined. 
Fore-feet, with four toes and six tubercles on the palm. Of the three anterior tubercles, 
one is seated at the common origin of the two middle toes, and one at the commencement of 
each of the other two toes, which arise farther back. The other three tubercles lie nearly in 
a line at the posterior part of the palm. The smallest of these is the interior one, and it 
occupies the usual site of the thumb, of which there is no other vestige,—not even a nail. 
