308 MONOGRAPHS OF NORTH AMERICAN RODENTIA. 
dress is worn for only about four months, the vernal change beginning in 
March; in the middle districts, about five months, and in the higher latitudes 
about six, where the winter dress, according to Dr. Richardson, is worn till 
the end of April. 
Summer specimens of var. virginianus from Massachusetts, New York, 
and Pennsylvania vary considerably in color through the varying intensity 
of the brown tints of the upper surface and the relative length of the black 
tips of the hairs. In some, the black tips are short and inconspicuous; in 
others, so long as to strongly vary the general color with black. The brown 
varies from pale yellowish-brown to dark reddish-brown, the brown tint of 
the under fur also similarly varying in intensity. The base of the under-fur 
varies from grayish to dark plumbeous. 
The exact ranges of varieties americanus and virginianus cannot now be 
well determined, and, as in the case of other intergrading geographical forms, 
can probably never be absolutely defined. According to Dr. Gilpin, the 
Nova Scotia type seems clearly referable to the northern form (var. ameri- 
canus). He describes the dorsal surface as being “sepia-brown, with a yellow 
wash”, and observes that they present none of the bright reddish or cinna- 
mon-brown mentioned by Professor Baird as characterizing more southern 
specimens. Dr. Gilpin’s description hence corresponds very nearly with 
specimens from the Red River district, and from Fort Rae, Great Slave Lake, 
and hence with Dr. Richardson’s description. 
In Table XVII, the first fourteen specimens, all from Massachusetts 
(Coll. M. C. Z.), and all in winter pelage, vary in length of body from 14 to 
20 inches; in length of hind foot, from 4.65 to 5.50; in length of ear, from 
2.40 to 3.60: the average being, length, 17.37; hind foot, 5.24; ear, 2.83. 
Fifteen other specimens (Coll. 8. L),* seven of which are also from Massa- 
chusetts, and the others from New York and Pennsylvania, range in length 
from 16 to 21 inches; hind foot, 4.57 to 5.68; ear, 3.00 to 3.60: averaging, 
length, 18.82; hind foot, 5.24; ear, 3.32. In length, the latter series exceeds 
the former by about one and a half inches, while the hind feet are equal; 
the difference in the length of the ear is nearly half an inch, one-half of 
which, at least, is due to the different way in which the measurements of the 
ear in the two series were taken, as shown by a remeasurement of some 
of the specimens of the latter series. 
In Table XVIII are presented the measurements of twenty-three 
* Measurements copied from Baird’s Mamm. N. Am. 
