_Description._--Size, small; back near Ochraceous-Buff, having black hair interspersed; mid-dorsal band not always well marked; sides Ochraceous-Buff with fine admixture of black hair; lateral line blending with Ochraceous-Buff of sides, not distinct; ventral surface white to base of hairs, in some cases lightly suffused with color of sides; tail indistinctly bicolored, tan to grayish-white below and brown above; hind feet grayish-white above; ears brownish, narrowly edged with Ochraceous-Buff; skull small; antorbital foramina relatively large; interorbital region broad; inferior ramus of the zygomatic process of the maxillary broad, often with medial projection; incisive foramina narrow posteriorly becoming broadly rounded anteriorly; palatal bridge relatively long; pterygoid fossae narrow; zygomatic arches relatively robust; nasals tapering at each end. _Comparisons._--From _Zapus princeps princeps_, _Z, p. luteus_ differs as follows: Size, smaller; color lighter, more Ochraceous-Buff; ears lighter, edged with Ochraceous-Buff as compared with white or yellowish-white; lateral line indistinct or wanting as opposed to distinct; dorsal stripe not well defined; interorbital region broader; antorbital foramina relatively larger; zygomatic arches more robust; nasals tapering at each end as opposed to parallel sided; auditory bullae smaller, less inflated. _Remarks._--The characters of this subspecies are relatively stable throughout most of its geographic range. Hall and Davis (1934:56) remarked that their material from the White Mountains of Arizona answered precisely to Miller's original description (1911:253) of the species, and my examination of these and other specimens from that area indicates the same thing except that the specimens average slightly darker mid-dorsally than those from New Mexico. _Zapus luteus australis_, based on a single individual taken in a riparian thicket along the Rio Grande at Socorro, New Mexico, is referable to _Z. p. luteus_. The diagnostic characters, referred to in the original description, are as follows: Small, slender, and very narrow skull; especially narrow braincase; slender rostrum; and light dentition. These are expressions of age, rather than of geographic variation, in that the individual is a subadult (young of the year). The color, which is paler than in adults of _Z. p. luteus_, is almost identical with that of a subadult (No. 205585 USBS) from Alpine, Arizona. I can see no basis for recognition of _Z. p. australis_ and the name, therefore, is placed as a synonym of _Z. p. luteus_.