Fur dusky gray above with a tinge of yellow; beneath cinereous: ears about half the length of the head.
Length of the head and body three inches two lines; of the head eleven lines; of the ears five lines; of the tail two inches eleven lines.
Head of a somewhat triangular form; muzzle pointed, sharper than in the M. sylvaticus: eyes and ears, especially the former, smaller than in that species; the latter oval, rounded at the extremity, and narrower in proportion to their length: whiskers shorter: tail stouter : feet and toes, particularly those behind, shorter. All the upper parts of the body and sides, dusky gray with a faint tinge of yellow, this last colour occupying a small portion of each hair near the summit, the basal half and extreme tip being dusky; under parts cinereous, paler than those above, likewise tinged with yellow: ears, feet, and tail, clothed with a very short fine hair; the last dusky, of one colour above and below. - Obs. The colours vary a little in different specimens, and sometimes individuals occur wholly white ; or white with dark spots.
Found in houses and stacks. Those which occur in the latter situation are remarkable for the brightness of their colour, which has a more decided yellow tinge than in house specimens. They also sometimes attain a larger size, measuring nearly four inches in length. Feeds on various animal and vegetable substances. Breeds several times in the year, and is extremely prolific.