_Diagnosis._--Size medium (see measurements). Color: Upper parts Snuff Brown, finely mixed with black; sides and flanks Sayal Brown; underparts overlaid with Cinnamon Buff, with suffusion of black on underfur; postauricular patches black, extending around ear; ears pointed and covered with black hairs; nose, cheeks, chin and top of head dusky; front feet, hind feet and distal part of tail white; tail covered proximally with light brown hairs. Skull: Moderately heavy and ridged; nasals long, wide posteriorly and not markedly dilated distally; posterior ends of nasals emarginate; zygomatic arches fairly widely spreading and angular, being nearly straight in adults, but tending to bow out slightly at posterior ends in young; zygomatic processes of maxillae heavy; interparietal small and variously shaped, but always wider than long; interorbital region fairly wide; well marked dorsal depression in frontals posterior to ends of nasals; interpterygoid space narrowly V-shaped; tympanic bullae large; occipital condyles large and widely separated; foramen magnum large and higher than wide; basioccipital wide; dentition light. _Comparisons._--From topotypes of _Thomomys talpoides moorei_, _wasatchensis_ differs as follows: Size slightly larger; ears longer and more pointed. Color: Generally darker throughout; postauricular patches smaller. Skull: Zygomatic arches not as widely spreading; zygomatic processes of squamosals dip farther ventrally; premaxillae less extended posterior to nasals; nasals wider posteriorly and less dilated distally; median dorsal depression of frontals present; tympanic bullae generally larger, but less inflated ventrally; foramen magnum larger especially in dorsoventral dimension; occipital condyles farther apart; basioccipital wider; alveolar length of upper molar series less; molariform teeth smaller; upper incisors wider and shorter. Topotypes of _wasatchensis_ differ from topotypes and near topotypes of _Thomomys talpoides uinta_ as follows: Size larger in every measurement taken. Color: Darker throughout; ears longer and more pigmented; opening of external ear smaller; postauricular patches larger. Skull: In females larger throughout, more massive and angular; nasals longer, wider and not so dilated distally; rostrum longer but wider; zygomatic arches wider, more angular and less widely spreading posteriorly; extension of premaxillae posterior to nasals less; tympanic bullae larger, but less inflated ventrally; foramen magnum larger and more ovoid; width across occipital condyles greater; basioccipital wider; molariform teeth smaller; upper incisors shorter and wider.