_Description._--Size, medium; back with broad mid-dorsal band, varying from pale brown mixed with Pinkish-Buff to dark brown mixed with Warm Buff or Ochraceous-Buff; sides varying from near Pinkish-Buff to near Ochraceous-Buff; ventral surface white to base of hairs, not suffused with other color; tail bicolored, pale brown above and white to yellowish-white below; ears dark, edged with white or yellowish-white; upper teeth divergent anteriorly; auditory bullae small; skull relatively long; zygomata relatively weak and not widely bowed; nasals wide posteriorly; pterygoid fossae relatively narrow. _Comparisons._--From _Zapus princeps nevadensis_, _Z. p. cinereus_ differs as follows: Size averaging smaller; entire coloration lighter; zygomata not so widely bowed; incisive foramina not so wide posteriorly; auditory bullae smaller; nasals wider posteriorly; pterygoid fossae narrower. From _Zapus princeps idahoensis_, _Z. p. cinereus_ can be distinguished by: generally paler color; smaller auditory bullae; broader interorbital region; anteriorly diverging tooth-rows; narrower pterygoid fossae. For comparison with _Zapus princeps utahensis_ see account of that subspecies. _Remarks._--Davis (1939:343) writes that "since _cinereus_ was described from nine specimens, only two of which are near adult, one cannot place much value on the coloration ascribed to it by Hall (1931:7)." I examined the type series and found, as did Davis (_loc. cit._), that the type is much lighter and grayer than is a near adult paratype, which was obtained the same day; however, I do not concur with Davis (_loc. cit._) that specimens from Mt. Harrison, 10 mi. S Albion, Idaho, which are darker and much more ochraceous than the paratype, necessarily are more nearly typically colored. These individuals, judged by cranial characters, are more nearly typical of _cinereus_ but show intergradation with _Z. p. idahoensis_ in their darker and more ochraceous pelage. Durrant (1952:387) found that the gray color of _Z. p. cinereus_ was not diagnostic in separating _Z. p. cinereus_ from _Z. p. utahensis_, because gray animals are also found in _Z. p. utahensis_. Specimens from Camp Tendoy, Pocatello, Idaho, are intermediate in color and in cranial characters as between _Z. p. idahoensis_ and _Z. p. cinereus_, but here are referred to _Z. p. cinereus_. Whitlow and Hall (1933:268) compared these individuals with specimens of _Z. p. princeps_ and _Z. p. cinereus_, finding them intermediate but in the aggregate of several differential characters better referred to the latter. _Specimens examined._--Total, 35, distributed as follows: IDAHO: _Bannock County_: Camp Tendoy, Pocatello, 2 (MVZ). _Cassia County_: Mt. Harrison, 10 mi. S Albion, 16 (MVZ).