_Comparisons._--Compared with topotypes of _Thomomys talpoides bridgeri_, _ravus_ differs as follows: Size larger; hind foot smaller; ears narrower. Color: Lighter throughout, grayish as opposed to brown. Skull: Smaller, narrower, less angular and less massive; nasals, rostrum, zygomatic processes of maxillae, ascending branches of premaxillae and posterior tongues of premaxillae all narrower; extension of premaxillae posterior to nasals longer; interparietal wider; braincase higher and narrower; tympanic bullae approximately the same size, but more inflated ventrally; interpterygoid space more narrowly V-shaped; upper incisors narrower; molariform teeth weaker. Compared with topotypes and near topotypes of _Thomomys talpoides uinta_, _ravus_ differs as follows: Size larger in every measurement taken. Color: Lighter throughout, being grayish as opposed to brown. Skull: Larger in every measurement taken; rostrum and nasals actually as well as relatively longer; extension of premaxillae posterior to nasals longer; upper incisors longer and wider; molariform teeth larger. There is only one other gray subspecies of _Thomomys talpoides_ in Utah, _Thomomys talpoides ocius_. Topotypes of _ravus_ differ from it as follows: Size markedly larger in every measurement taken. Color: Darker, more brown hairs. Skull: Larger in every measurement taken; premaxillae extended farther posteriorly to nasals; extension of supraoccipital posterior to lambdoidal suture markedly less; tympanic bullae actually as well as relatively smaller; upper incisors longer and more procumbent. This new subspecies can be readily distinguished from all other subspecies of _Thomomys talpoides_ occurring in Utah by markedly greater size and paler, more grayish color. _Remarks._--The range of this form appears to be limited to the north slopes of the Uinta Mountains, except in Daggett County where it occurs also on the south slopes. Intergradation in color and in cranial details with _bridgeri_ is shown by animals from the East Fork of Blacks Fork, thirty-one miles SSW Fort Bridger, and by those from Henrys Fork, 8,300 ft., both in Summit County. Due to the grayish color and the narrower, weaker skull they are referred to _ravus_. Intergradation with _uinta_ is shown by specimens from the type locality of the latter race. The type series of _uinta_ consists of intergrades between _ravus_ and the animals to the west and south (see remarks under _uinta_). It is doubtful whether _bridgeri_ occurs in Utah. Material from Rich County and extreme northern Cache County would settle the question. Perhaps _bridgeri_ is restricted to the lower valleys in southwestern Wyoming. Two specimens from northern Cache County, from Logan Canyon, Beaver Basin, Utah-Idaho Line appear to be intergrades between _bridgeri_ and _wasatchensis_, but are referable to the latter race.