MAMMALS OF MINNESOTA. 



189 



Vesperimus sonoriensis LECONTE . 



THE SONORA MOUSE. 



Mus leucopus RICHARDSON, Zool. Journ., 1818; Fauna Bor. Am., 1829. 

 Hesperomys sonoriensis LECONTE, Proc. Acad. Nat. Sci. Phila., 1853. 



AUDUBON AND BACHMAN, Quad. North America, 1854. 



BAIRD, Mam. K A., 1857; U. S. and Mex. Bound. Surv.,1859. 

 Hesperomys leucupus sonoriensis COUES, Monogr. N. Am. Rodentia, 1877. 



The little animal known as Hesperomys sonoriensis is a resident 

 of the western interior region and might be regarded as a per- 

 manent prairie variety of H. leucopus but for the fact that the 

 two species are associated at the limits of their geographical 

 range instead of fading insensibly into each other as geographical 

 varieties of recent origin might be expected to do. Our collec- 

 tion embraces a considerable number of specimens collected at 

 Brown's Valley and other points near the western line of Min- 

 nesota where this form is the most abundant mouse. There is 

 a very remarkable uniformity in size and coloration which both 

 are sufficiently unlike the deer mouse to be easily distinguish- 

 able. On the whole, the colors may be said to be considerably 

 lighter and less conspicuous than in the deer mouse, but still 

 they are bright and attractive. The white parts encroach 

 more upon the dorsal area than in our more eastern mouse and 

 the line of demarkation is more distinct, there being none of 

 the gray on the hips usually seen in the latter, and the sides and 

 lower parts are beautifully white. The brown portion of the 

 tail is a narrow stripe and the back is not so conspicuously 

 marked with black hairs as in leucopus. Besides these differ 

 ences in the whole anterior portion, the pelage is sifted over 

 with whitish so as to give it a grayish tinge, while only on the 

 rump is found the bright reddish brown of our familiar species. 

 Should the color not prove distinctive the marked difference in 

 size is sufficiently conspicuous. 



The following table fairly represents the limits of normal 

 variation and in one case (No. 100) a specimen to some extent 

 resembling the deer mouse. 



