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.