_Description._--Size, medium; color moderately dark; upper parts noticeably dull and dusty; broad dorsal band of dull Ochraceous-Buff to near Warm Buff sprinkled with black hair to a varying degree, resulting in two color phases (dark has more black hair; Ochraceous phase or Warm Buff phase has more brown hair); sides paler than back owing to fewer black hairs; lateral line, when present, narrow and dull; ventral surface pure white; tail bicolored, pale brown above, yellowish-white to dull white below; ears dark with narrow white or yellowish-white edgings; feet white above; skull narrow across zygomata; incisive foramina narrow; bullae moderately inflated; nasals narrow at tips; postpalatal notch anterior to posterior face of last molars; braincase moderately narrow; zygomatic arch short. _Comparisons._--From _Zapus princeps saltator_, _Z. p. kootenayensis_ differs as follows: Upper parts generally dull with less ochraceous; sides with more yellow, less ochraceous; lateral line wanting or not bright; skull averaging slightly smaller; incisive foramina smaller and narrower posteriorly; small medium projection on inferior ramus of the zygomatic process of maxillary frequently present instead of absent; pterygoid fossae shorter and narrower. For comparison with _Zapus princeps idahoensis_ see account of that subspecies. _Remarks._--This subspecies is paler and averages smaller than either of the subspecies with adjoining geographic ranges. There is intergradation with _Zapus princeps idahoensis_ in color, shape and size of incisive foramina, and in the shape of the nasals in Idaho-taken specimens from Glidden Lakes and Enaville. These individuals are thought to be _Z. p. idahoensis_. Specimens from the same state taken at Cascade Creek and 13 mi. E and 5 mi. N Coeur d'Alene show intergradation in color, size and inflation of bullae, configuration of nasals, and shape of the vomer between _Zapus princeps idahoensis_ and _Z. p. kootenayensis_. The majority of characters studied show these animals to be referable to _Z. p. idahoensis_. Specimens from Monashee Pass, 4000 ft., British Columbia, show relationship to _Zapus princeps saltator_ in the posteriorly wide incisive foramina, in the narrow vomer, and, in some individuals, in the increased amount of ochraceous, dorsally and laterally. The majority of characters studied show these animals to be referable to _Z. p. kootenayensis_.