_Specimens examined._--Total, 38, distributed as follows: _Summit County_: Henrys Fork, 8,300 ft., 8; E Fork, Blacks Fork, 31 mi. SSW Fort Bridger, 4 (C. M.). _Daggett County_: Vernal-Manila Road, 4 mi. W Green's Lake, 7,500 ft., 6 (C. M.); Elk Park, Uinta Mountains, 5 (B. Y. U.). _Uintah County_: Trout Creek, SE Trout Peak, 22 mi. NW Vernal, 9,300 ft., 5 (C. M.); Vernal-Manila Highway, 19 mi. N Vernal, 8,000 ft., 6 (C. M.); Taylor Peak, 17 mi. N Vernal, 4 (C. M.). =Thomomys talpoides ocius= Merriam _Thomomys clusius ocius_ Merriam, Proc. Biol. Soc. Washington, 14:114, July 19, 1901. _Thomomys clusius_ Allen, Bull. Amer. Mus. Nat. Hist., 13:246, November 25, 1896. _Thomomys ocius_ Bailey, N. Amer. Fauna, 39:107, November 15, 1915; Barnes, Bull. Univ. Utah, 12 (No. 15):83, April, 1922; Bull. Univ. Utah, 17 (No. 12):102, June, 1927. _Type._--Male, adult, skin and skull, No. 18852/25586, U. S. National Museum (Biological Surveys Collection); dry sagebrush mesas at Harveys Ranch, Smiths Fork, 6 mi. SW Fort Bridger, 6,657 ft., Uinta County, Wyoming; May 24, 1890; collected by Vernon Bailey; original number 1194 (after Bailey, type not seen). _Diagnosis._--Size small (see measurements). Color: Upper parts Tilleul Buff overlaid with Avellaneous, grading over sides and flanks to nearly white on underparts; underparts with faint wash of creamy white; postauricular patches small and dusky and completely circling the ear; nose and cheeks dusky; front feet, hind feet, throat, ventral surface of tail and distal half of tail white. Skull: Small, slender but compact; nasals rounded posteriorly; extension of premaxillae posterior to nasals very short; zygomatic arches robust, but not widely spreading, widest posteriorly; interparietal large and pentagonal in shape; extension of supraoccipital posterior to lambdoidal suture long; tympanic bullae actually as well as relatively large; basioccipital narrow; pterygoid hamulae long and ridged; upper incisors short and strongly recurved. _Comparisons._--Compared with one topotype and seven near topotypes of _Thomomys talpoides pygmaeus_, _ocius_ differs as follows: Size larger in every measurement taken. Color: Lighter throughout, grayish as opposed to brown; distal half of tail white as opposed to only a few white hairs at tip of tail. Skull: Larger in every measurement taken; skull more compact; zygomatic arches heavier and more widely spreading posteriorly; tympanic bullae larger; upper incisors larger, but equally strongly recurved; molariform teeth larger.