138 MONOGRAPHS OF NORTH AMERICAN RODENTIA. 
perceptible. The under parts are dull white, much soiled, with a weak shade 
of the yellowish clay-color of the sides, and the ashy of the bases of the 
hairs is always more or less apparent. The luteous shade of the under parts 
is sometimes almost as strong as on the sides, especially across the abdomen. 
Between the thighs and arms, and under the throat, a whiter and ashier shade 
prevails. The tail is distinctly bicolor, but not very sharply so; the under 
surface is like the belly or rather yellower, the upper like the back or rather 
darker. There are no definite markings about the head; but a slight dusky 
area frequently observable about the eyes, and a sort of stripe of dusky along 
the nose, sometimes suggest a certain particoloration there. The upper sur- 
faces of the hands and feet are nearly white. 
We should not omit to add that the pelage is everywhere long, full, soft, 
and mollipilose, with but little admixture of lengthened bristly hairs, thus 
affording efficient protection from the rigors of the winter of high climates. 
There is a tangible difference in this regard in the more southern varieties. 
We have great pleasure in adding this interesting animal to our fauna, 
our only previously-recorded form being the var. gapperi, and the Mus rutilus 
of Pallas being supposed to be confined to the north of Europe and Asia. 
Of the correctness of our identification there can be absolutely no question 
whatever. We have carefully compared our North American series with 
specimens from Lapland and Kamschatka, and they prove identical. All the 
differences supposed to mark the North American ‘‘Hypudzeus” disappear in 
the Arctic series below given, being only applicable to the series from the 
Northern United States and adjoining regions; and they are, we hold, only 
indicative of a climatic differentiation. We challenge the proof that Mus 
rutilus is not a cireumpolar species, which, south of a certain isothermal, has 
become modified into what is known in North America as “Hypudeeus gap- 
’ 
peri” and in Europe as ‘“ H. glareola” and “H. rubidus”. 
Professor Baird says, of the skulls of “‘Hypudeeus” he examined, that 
that of gapperi “bears a very close resemblance to that of Arvicola rutilus ; 
so close, indeed, that *  * Jam unable to indicate reliable characters to 
separate specimens from Massachusetts and Lapland”. We are able to 
include glareola in the same statement, and to prove, by the following table 
of measurements, that there are no cranial or dental differences whatever in 
the three supposed species. 
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