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.
Specimens examined.—Total, 38, distributed as follows: Summit County: Henrys Fork, 8,300 ft., 8; E Fork, Blacks Fork, 31 mi. SSW Fort Bridger, 4 (C. M.). Daggett County: Vernal-Manila Road, 4 mi. W Green's Lake, 7,500 ft., 6 (C. M.); Elk Park, Uinta Mountains, 5 (B. Y. U.). Uintah County: Trout Creek, SE Trout Peak, 22 mi. NW Vernal, 9,300 ft., 5 (C. M.); Vernal-Manila Highway, 19 mi. N Vernal, 8,000 ft., 6 (C. M.); Taylor Peak, 17 mi. N Vernal, 4 (C. M.).
Thomomys talpoides ocius Merriam
Thomomys clusius ocius Merriam, Proc. Biol. Soc. Washington, 14:114, July 19, 1901.
Thomomys clusius Allen, Bull. Amer. Mus. Nat. Hist., 13:246, November 25, 1896.
Thomomys ocius Bailey, N. Amer. Fauna, 39:107, November 15, 1915; Barnes, Bull. Univ. Utah, 12 (No. 15):83, April, 1922; Bull. Univ. Utah, 17 (No. 12):102, June, 1927.