RODENTIA—MURINAE—HESPEROMYS MICHIGANENSIS. 477 
This is, perhaps, the smallest species of Hesperomys found within the limits of the United 
States, and possesses certain characters by which it may be readily distinguished from its allies. 
The ears and feet are smaller than in H. leucopus, the latter conspicuously so; the tubercles of 
the soles are large; the posterior, however, small and conical, its anterior base posterior to a 
point half-way from the heel to the balls of the toes. The soles are densely coated with hair 
from the heel to the posterior tubercles. 
The shortness of the hind foot is seen in the approximation of the tubercles of the soles ; 
thus the posterior tubercle is as near to the first anterior on the inner edge as to the first outer, 
while in H. leucopus it is considerably nearer to the first outer. 
The tail is short and conical, rather thick at the base; it is but little longer than the body 
alone—considerably shorter than the head and body together. It is well coated with short 
hairs, concealing the annuli. 
The prevailing color of this species is a dark brown, sometimes almost black in young speci- 
mens, always with a distinct stripe of darker, about the width of the head, along the middle 
of the back. In old specimens there is usually a mixture of yellowish brown on the sides, but 
the tint is never so conspicuous as in H. leucopus. The cheeks often show a rather brighter 
shade of the same. The ears are dark brown. The dusky of the sides extends beyond the 
wrist, usually as far as the bases of the fingers; the upper part of the hind feet is also dusky 
to the toes. The under parts are generally snowy white, the color strongly defined against 
that of the sides; the tail is dusky above and white beneath. In some specimens the plumbeous 
base of the fur shows through the white tips, so as to impart an ashy tint. 
This species is at once distinguishable from the H. leucopus by the much darker color at all 
ages, the shorter ears and hind feet, and the dusky surfaces of the feet. The dusky specimens of 
HI, leucopus are without the broad central wash of darker. The shade of color is much like the 
dark varieties of H. austerus, but in this species there is not the distinct line of darker on the 
back ; the feet are snowy white ; the ears and hind feet much larger. 
Mr. Kennicott distinguishes a Mus bairdii from the M. michiganensis by the strong contrast 
of color between the belly and sides in the former, as compared with the more ashy color 
beneath, and indistinct separating line in the latter. In the specimens before me are two of 
larger size than the majority of short dusky-footed ones, and having the characters indicated as 
belonging to MZ. michiganensis, but Iam not able to appreciate any other differences; and the 
same features are observable in some of the smaller ones. Still, I have much confidence in the 
judgment of so able a naturalist as Mr. Kennicott, supported as he is by Dr. Hoy. The MW. 
michiganensis is said to inhabit open woods near Racine, and not to be found at West Northfield, 
which is strictly prairie in its character. For the present, however, I shall consider them the 
same.} 
1 Since writing the preceding article, I have received a note from Dr. Hoy, in which he says: ‘‘I consider the difference 
between the oak opening deer mouse (michiganensis) and the prairie deer mouse (bairdii) to consist mainly in the more 
uniform color, longer tail and larger head of the former, giving to it the look more of the common house mouse than the 
latter. The bairdii has a black stripe on the back ; the white belly is separated from the yellowish fawn color of the sides 
by a distinct line of demarcation.’’ 
“One thing is certain—we find one species in the openings, while the other is confined to the prairie ; so far, at least, as 
I have observed.” 
Ii is quite possible, after all, that none of the specimens before me belong to the H. michiganensis, as restricted by Messrs. 
Hoy and Kennicott. 
