658 MONOGRAPHS OP NORTH AMERICAN RODENTIA. 



Two specimens collected on the Northwestern Boundary Survey by Dr. 

 Kennerly (doubtless iii Washington Territory) can be exactly matched, both 

 in size and color. I>\ specimens from Malamagaminque, Canada, excepl that 

 one is more yellow below than the Canada specimens. Another, from Fort 

 Crook, Cal., is much darker than the specimens from Washington Ter- 

 ritory, with a strong yellowish wash below, which extends over the whole 

 lower sml'ac<! of the tail. No. !ib'"25, 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. 

 rir.hfirdsoni of the Sciurus hudsonius group, inhabiting the same region. 

 Neither this form {Pt&romys 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, 1 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 



