90 MONOGRAPHS OF NORTH AMERICAN RODENTIA. 
fore legs to the hands The under parts are pure white, as usual, with pretty 
distinct line of deniarkation along the sides. The tail, along its dorsal aspect, 
is much paler than usual, agreeably with the general hue of the upper parts ; 
but, on the contrary, it is so much darker than usual underneath that it appears 
nearly uaicolor, aud, at any rate, there is no definite line of separation of the 
two shades of color. 
3 The soles of the feet present the extreme condition of nakedness as yet 
observed in any North American species of the genus. There is a light hairy 
fringe all along the sides; but at least a central median space, perfectly denuded, 
may be traced to the very heel. But this character, at first sight apparently 
so distinctive, is, as just intimated, merely the extreme of an insensible grada- 
tion from the dense hairiness of specimens from northern cold regions, and is 
strictly agreeable to a well-known law. E 
The ear will average a little longer than in /eucopus, and corresponds 
with the feet in its scantier hairiness. The tail, likewise, is scant-haired, 
revealing the annuli very plainly. In length, this member will average con- 
siderably over the average of /eucopus; but still it falls short of the extreme 
of the latter, as witnessed in Vermont ‘myoides” and Washington Territory 
“Doylii”; and in the six specimens before us it varies in length about an inch ; 
thus, it is, in No. 1581, nine-tenths of an inch longer than the head and body, 
and, in 1336, it is two-tenths of an inch shorter than the head and body. 
Since the foregoing remarks upon H. eremicus were penned, we have 
handled an interesting and highly instructive series of skins from Camp Grant, 
sixty miles east of Tucson, Ariz., collected by Dr. Palmer. This series con- 
firms our views by furnishing the stepping-stones before lacking, and proves 
that eremicus slides insensibly into the ordinary western form, of which it is, 
therefore, a geographical differentiation. 
Of the twenty-two specimens in the series now lying before us, twelve 
are referable to eremicus; these are measured in the foregoing table. Of 
these twelve, eight or nine are pure typical evemicus, agreeing in having per- 
fectly naked soles, very large, leafy, nearly naked ears, the scant-haired indis- 
tinctly bicolor tail about equal to the head and body (or, if anything, rather 
longer than shorter), and the coloration of the peculiar pinkish or ochrey- 
fulvous mixed on the back with quite black hairs; thus being identical with 
the original types of eremicus. 'The individual variations in these eight or nine 
specinens are quite as usual in any species or variety of the genus. In two 
