52 MONOGRAPHS OF NORTH AMERICAN RODENTIA. 
“a 
upon to prove the position we assume regarding certain nominal species, that 
no detailed description is required in this connection. Some general observa- 
tions, however, will not be out of place here. 
The under parts of the adult animal are snowy white, and this includes 
the upper surfaces of both fore and hind feet to the wrist and ankle, and 
usually the greater part of the outside of the fore leg also, so that the sharp 
line of demarkation between the white and the color of the upper parts gen- 
erally passes in a pretty straight line by the shoulder along the side of the 
neck and side of the head, a little below the eye, to the snout. But the 
extension of color down the fore leg is utterly indefinite, for two reasons :— 
first, in the young, while still gray, the color normally reaches the paws, and 
its subsequent restriction is a matter of gradual change with age; yet a great 
many individuals do not seem to perfect this change, but remain for some 
seasons at least in the same condition ; and, secondly, many young ones have 
the outside of the legs as largely white as they ever become in the old. As 
a specific character, therefore, this feature is not of the slightest consequence. 
In general, the color of normal adult examples, as No. 1434 from Massa- 
chusetts, is a rich fawn, with a pretty well defined dorsal darkening length- 
wise from occurrence of black-tipped hairs along the back. But this ‘‘typical” 
coloration is expressed in noticeably few of the specimens that make up an 
average miscellaneous lot—probably not one in six; while the departures from 
it defy description. : 
This is, moreover, independent of the normal regular change of pelage 
with age. The young are at first plumbeous-gray above and ashy-white 
below, without a trace of brown or fulvous shade ; this has to change gradu- 
ally into the hue given in the last paragraph. Ina considerable proportion of 
specimens, the change is observed to begin along the sides as an indistinct 
stripe of fulvous; and this progresses until the whole pelage is changed. 
This lateral stripe is sometimes pretty sharp, but oftener merges insensibly 
into the gray color; so that we are unable to lay down any appreciable stages 
in the transition. 
It is also highly probable that a considerable percentage of individuals 
pass their whole lives in a pelage nearer gray than fawn color; and it is 
unquestionable that the animal can and does breed in such condition. 
In the vast majority of instances, the tail is pretty sharply bicolor—white 
underneath, and on top corresponding in color to the back. The dark area 
