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 

 J3", 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 M. michiganensis, but I am 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 M. 

 michiganensis is said to inhabit open woods near Kacine, 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 



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. ' ' 



It is quite possible, after all, that none of the specimens before me belong to the If. michiganensis, as restricted by Messrs. 

 Hoy and Kennicott. 



