676 MONOGRAPHS OF NORTH AMERICAN RODENTIA. 
the toes being naked. The gencral pelage is also much fuller, longer, and 
softer in winter than in summer. 
The skull presents the usual range of individual variation so often noted 
in these papers, especially in respect to the form of the nasal bones. ‘These 
vary greatly in width, especially posteriorly, and also in respect to length. 
In skulls of the same general size, the width of the nasals posteriorly varies 
from 0.10 to 0.15 of an inch, or nearly 33 per cent. of the average width. 
They also vary greatly in respect to their posterior outlines, being generally 
more or less emarginate, but vary from squarely truncate to deeply emarginate. 
As already noted in the general remarks upon the genus Sciwrus, the first 
premolar is generally present, though often so minute as to readily escape 
detection. I find it more frequently present in New England specimens 
than in those from Fort Simpson, H. B. T. In the former, it is to be found 
in about two specimens out of three; in the latter, in only about one in six! 
It is also pretty unifurmly present in Pennsylvania specimens. 
As shown by the subjoined tables of measurements, northern specimens 
are considerably larger than southern ones. Specimens from Minnesota, and 
thence westward to the Black Hills, appear to be larger than those from the 
Fur Countries, as often happens in other species of North American Mammals. 
On the other hand, Pennsylvania specimens are larger than those from 
Massachusetts, New Hampshire, and Maine. Taking the skulls as a basis 
for comparison, twelve skulls from Upton, Me., have an average length of 
1.73, while ten skulls from Greensburg, Pa., average 1.80. Ten others 
from Fort Simpson, H. B. T., average very nearly 1.85, or 0.12 (about one- 
seventh) more than those from Maine. The length of fully adult specimens 
from Maine and New Hampshire (measured from the end of the nose to the 
base of the tail) rarely exceeds 6.75, and very often falls below 6.50; 
Massachusetts specimens frequently exceed 7.00, and not often fall below 6.75 
while Pennsylvania specimens are still larger. Specimens from the Fur 
Countries are still larger, apparently averaging 7.75. 
In respect to other geographical variations, specimens from high northern 
localities are paler and more fulvous than those from the United States, and 
are more annulated beneath with black. The brightest or reddest specimens 
in the collection are from New York, Pennsylvania, and Ohio, in which, also, 
annulations below are infrequent. New England specimens are scarcely 
different in color from those from the Middle States; Maine specimens being, 
