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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.

Topotypes of wasatchensis can be distinguished from those of Thomomys talpoides oquirrhensis as follows: Size larger; tail longer; ears longer. Color: Slightly darker on sides and underparts. Skull: Heavier, more ridged and angular; nasals more dilated distally; posterior ends of nasals more deeply emarginate; zygomatic arches heavier and more widely spreading, but more nearly parallel and less divergent posteriorly; zygomatic processes of maxillae much heavier; braincase and tympanic bullae larger; pterygoid hamulae shorter; interpterygoid space more narrowly V-shaped; wider across occipital condyles; foramen magnum larger and more ovoid.

From topotypes of Thomomys talpoides gracilis, wasatchensis differs as follows: Size larger; hind foot longer; ears longer and more pointed. Color: Darker throughout; postauricular patches relatively smaller. Skull: Larger, heavier and more angular; nasals emarginate posteriorly as opposed to truncate; rostrum heavier; zygomatic arches heavier and more widely spreading; zygomatic processes of maxillae much heavier and more angular; mastoid breadth greater; interparietal relatively smaller; extension of premaxillae posterior to nasals actually as well as relatively less; palatal pits deeper; tympanic bullae larger; interpterygoid space more narrowly V-shaped; foramen magnum more ovoid; upper incisors wider.

Topotypes of wasatchensis can be readily distinguished from those of Thomomys talpoides levis and parowanensis by larger size; more massive, ridged, angular skulls; larger tympanic bullae; large, ovoid foramen magnum; and relatively smaller interparietal.

Remarks.—Specimens from Mount Timpanogos and environs are intergrades between moorei and wasatchensis. They resemble moorei in the shape and size of the tympanic bullae, and are intermediate in the size and shape of the foramen magnum. In the majority of characters they resemble wasatchensis to which they are here referred. The animals from east of Salt Lake City in Salt Lake County are intergrades between oquirrhensis and wasatchensis and show some characters of uinta, but are referable to wasatchensis. Animals from Morgan County and western Summit County are intergrades between wasatchensis and uinta. They resemble uinta in size, shape of nasals and size of tympanic bullae. The remainder of the cranial details place them with wasatchensis. Morphologically the animals from Wellsville, Cache County, were the closest to the topotypes of any obtained and are nearly indistinguishable from them. Like the topotypes of wasatchensis this population inhabits a high valley. The remaining specimens from Cache County resemble those from Morgan and Summit counties.

Thomomys talpoides oquirrhensis Durrant

Type.—Male, adult, skin and skull; No. 2605, Museum of Zoölogy, University of Utah; Settlement Creek, Oquirrh Mountains, 6,500 ft., Tooele County, Utah; June 11, 1938; collected by S. D. Durrant; original number 1461.

Range.—Known only from the Oquirrh Mountains, which are in Salt Lake, Tooele and Utah counties, Utah.

Diagnosis.—Size medium (see measurements); ear long; tail short, claws of front feet long and slender. Color: Upper parts Buckthorn Brown, mixed with black, grading over the sides and flanks to Pinkish Buff on the ventral surface; feet white; nose grayish black; postauricular patches medium in size and black; chin and throat with varying amounts of white; proximal two-thirds of tail dark brown, distal third