190 BULLETIN NO. VII. 
There is no evidence, so far as our state is concerned, that 
the three species of Vesperimus merge into each other. V. 
michiganensis and V. sonoriensis are associated westwardly and 
although the exact line of contact between the latter and V. 
leucopus has not been studied it is presumable from appear- 
ances that this line corresponds with the western forest limit 
- and is quite sharp. 
The westward range of the species includes Dakota, Mon- 
tana, Wyoming, Nebraska, Kansas, Colorado, Utah, Arizona, 
New Mexico, Texas. and part of California. 
The Arctic mice of this group resemble the present species in 
having short tails but fora reason quite different from that 
which would by assumed in this case. The color, moreover, 
in the latter is darker. The matter of coloration is so largely 
dependent on the humidity of the climate that our western 
mice, at least within the influence of the Red River valley, are 
much darker than typical V. sonoriensis of the plains. Of the 
habits we know nothing to distinguish them from the common 
deer mouse. They may be seen springing about among the 
high grass at times although probably less saltatorial than the 
deer mouse. | 
Vesperimus michiganensis AUD. AND BACH. 
THE MICHIGAN MOUSE. 
(Plate XI.) 
Mus michiganensis AUDUBON AND BACHMAN, Journ. Acad. Nat. Sci. 
Phila., 1842 ; Quadrupeds N. A., 1854. 
Hesperomys michiganensis WAGNER, Wieg. Archiy., 1843. 
BAIRD, Mam. N. A., 1857. 
Hesperomys (Vesperimus) michiganensis Cours, Proc. Acad. Nat. Sci. 
Phila., 1874; Monogr N. A. Rodentia, 1877. 
Mus bairdii Hoy and KENNIcoTT, U.S. Pat. Offic. Rep. Agric., 1856. 
The Michigan mouse is common throughout the upper Mis- 
sissippi valley and the states adjoining and is of reasonably 
frequent occurrence in the south eastern parts of Minnesota. 
This mouse may be at once distinguished from the deer mice 
by its small size, small tail and feet and the darker coloration. 
Unless examined carefully the color will usually seem not 
greatly brighter than in the house mouse. The general gray 
of the upper parts is mingled with yellowish on the sides, 
especially upon the cheeks, as Audubon points out, while the 
whole back is very dark brown. (The colors are rather 
brighter than usual in our drawing.) The gray of the sides 
extends down the outside of the limbs to the wrist and ankle. 
