658 MONOGRAPHS OF NORTILT AMERICAN RODENTIA. 
Two specimens collected on the Northwestern Boundary Survey by Dr. 
Kennerly (doubtless in Washington Territory) can be exactly matched, both 
in size and color, by specimens from Matamagaminque, Canada, except that 
one is more yellow below than the Canada specimens. Another, from Fort 
Crook, Cal., is much darker than the specimens from Washington 'er- 
ritory, with a strong yellowish wash below, which extends over the whole 
lower surface of the tail. No. 9625, from Idaho, and No. 9704, from, the 
Uintah Mountains, are two of the darkest specimens in the collection; but 
in the series from Big Island, Great Slave Lake, there is one fully as dark, 
while one from the Red River district is scarcely lighter. 
Specimens from the United States, and especially from the more south- 
ern portions, are more yellowish-brown above, with much less black on the 
tail, and more yellowish below, than specimens from Northern New England, 
Canada, and the more boreal parts of the continent. In some of the southern 
specimens, there is no dusky or black on the tail, which inclines to a rufous 
shade of brown above and yellowish-brown below. 
Average southern specimens differ from average northern specimens 
most strikingly in size. and in the length and fullness of the pelage, but also 
in the tail being relatively narrower, and the soles of the feet nakeder, and 
also quite appreciably in color, especially in the upper side of the tail being 
nearer of the color of the back. There is, however, no break in the sequence 
from north southward, either in size, color, or other characters, by which the 
group can be subdivided specifically, or even varietally. The recognition, 
as above, of a northern and southern subspecies, is, in great measure, arbitrary. 
Apparently, those inhabiting the Rocky Mountains of Montana and the Uintah 
Mountains are darker in color than those from other regions, and rather more 
ferruginous above, running into a phase corresponding somewhat with var. 
rithardsoni of the Sciurus hudsonius group, inhabiting the same region. 
Neither this form (Pteromys alpinus auct.) nor the so-called ‘‘Pteromys 
oregonensis” seems to me to be varietally distinguishable, especially the latter, 
specimens of which are, sometimes at least, absolutely indistinguishable from 
Canadian specimens. The supposed differences in the length and direction 
of the carpal fascia supporting the flying-membrane, I am unable to appreciate. 
In respect to differences of a strictly individual character, we meet 
occasionally with specimens from both the Atlantic and. Pacific slope, as well 
as from the interior, in which the color of the lower surface of the tail is 
