_Description._--Size, large; back from Cinnamon-Buff to Warm Buff overlaid with black hairs; sides lighter with less admixture of black hairs; lateral line indistinct, sometimes wanting; tail bicolored, brownish-black above, white to yellowish-white beneath; feet grayish-white above; ventral surface white to base of hairs; ears dark, edged with white to yellowish-white; skull large; palatal bridge relatively short; upper tooth-rows diverging anteriorly; occipitonasal length great; interorbital region broad; zygomata widely bowed; postpalatal notch anterior to posterior face of last molars; mastoid width great. _Comparisons._--From _Zapus princeps princeps_, _Z. p. utahensis_ differs in: color dorsally and laterally less ochraceous, lacking broad lateral line; skull larger in every part measured, excepting length of palatal bridge and breadth of palate at M3; zygomata more bowed; upper tooth-rows more divergent anteriorly; postpalatal notch anterior to posterior border of last molars. Compared with _Zapus princeps cinereus_, _Z. p. utahensis_ differs as follows: Size averaging larger; upper parts darker, Cinnamon-Buff not Pinkish-Buff; incisive foramina wider posteriorly; palate wider; zygomata more robust. For comparison with _Zapus princeps idahoensis_ see account of that subspecies. _Remarks._--_Zapus princeps utahensis_ most closely resembles the several subspecies in the Great Basin in its large size, widely bowed zygomata, and posteriorly broadened incisive foramina. Intergradation between _Z. p. utahensis_ and _Zapus princeps cinereus_, geographically the nearest of the Great Basin subspecies, is not known. Intergradation in color and cranial characters occurs between _Zapus princeps idahoensis_ and _Z. p. utahensis_ in specimens from 17 mi. E and 4 mi. N of Ashton, Idaho. All these specimens are, however, referable to _Z. p. idahoensis_. Animals from 9 mi. SE Irwin and from 3 mi. SW Victor, Idaho, resemble _Z. p. utahensis_ in most differential characters (dorsally ochraceous, lateral line more distinct, incisive foramina large, palate broad anteriorly, auditory bullae less inflated), and are here referred to _Z. p. utahensis_. A series of specimens from the head of Crow Creek, Idaho, were considered by Davis (1939:340) to be intergrades between _Z. p. idahoensis_ and _Z. p. utahensis_; he thought that the specimens were more nearly like _Z. p. utahensis_ in color, but cranially (80 per cent in average ratio of anterior width of palate to posterior width of palate), more nearly like _Z. p. idahoensis_, to which subspecies he referred them. I have examined these specimens and find them to be more nearly like _Z. p. utahensis_ not only in color but in cranial characters as well. For example, the average ratio obtained by me for anterior width of palate to posterior width of palate is 72 per cent, rather than 80 per cent as given by Davis (_loc. cit._). Other cranial characters, size of the incisive foramina, shape of the foramen