Large size is the distinctive feature of _Thomomys bottae lenis_. The skulls are the largest of any species or subspecies of _Thomomys_ found in Utah. In total length, however, these animals are no longer than the extremes found in other named races. When Goldman (1942:75) described this race as new, he referred it to the species _Thomomys townsendii_, but remarked that the animal from Richfield was different enough from any other form then named to merit probably full specific status. I know of no character other than size to separate _Thomomys townsendii_ from _Thomomys bottae_, and since intergradation has been shown to exist between these alleged _townsendii_ from Richfield and animals from extreme western Utah known to belong to the species _bottae_, _lenis_ is here arranged as a subspecies of _Thomomys bottae_ which name has priority over _Geomys townsendii_. The range here ascribed to this race is the Sevier River Valley from Piute County as far downstream as the town of Lynndyl which is near the eastern mainland of Pleistocene Lake Bonneville. The Sevier River continues farther out into Delta Valley ultimately to empty into Sevier Lake, which at present is adjacent to the area that formerly constituted the western mainland of the aforementioned ancient lake. This watercourse may have provided a migration route in ancient times, during the fluctuations of Lake Bonneville, whereby the animals formerly of the western mainland were able to come far eastward. The animals from Lynndyl which are intergrades between _lenis_, an eastern mainland form, and _centralis_ and _aureiventris_ which are western mainland forms of Lake Bonneville lend support to this hypothesis. _Specimens examined._--Total, 26, distributed as follows: _Millard County_: Lynndyl, 4,796 ft., 21. _Juab County_: U. B. (= Yuba) Dam, 5,000 ft., 1. _Sevier County_: Salina, 4,575 ft., 1; Richfield, 5,308 ft., 3. (U. S. N. M.). =Thomomys bottae levidensis= Goldman _Thomomys bottae levidensis_ Goldman, Proc. Biol. Soc. Washington, 55:76, June 25, 1942. _Thomomys perpallidus aureus_ Bailey, N. Amer. Fauna, 39:75, November 15, 1915; Barnes, Bull. Univ. Utah, 12 (No. 15):85, April, 1922; Bull. Univ. Utah, 17 (No. 12):100, June, 1927. _Type._--Male, adult, skin and skull, No. 191962, U. S. National Museum (Merriam Collection); Manti, 5,500 ft., Sanpete County, Utah; December 6, 1888; collected by Vernon Bailey; original number 427 (after Goldman, type not seen). _Range._--San Pitch River Valley, Sanpete County, Utah.