=Thomomys talpoides gracilis= Durrant _Thomomys quadratus gracilis_ Durrant, Bull. Univ. Utah, 39 (No. 6):3, February 28, 1939. _Thomomys talpoides gracilis_ Durrant, Bull. Univ. Utah, 30 (No. 5):6, August 24, 1939; Goldman, Journ. Mamm., 25:414, December 12, 1944. _Thomomys quadratus fisheri_ Hall, Univ. California Publ. Zooel., 37:4, April 10, 1931. _Thomomys uinta_ Bailey, N. Amer. Fauna, 39:114, November 15, 1915; Barnes, Bull. Univ. Utah, 12 (No. 15):83, April, 1922; Bull. Univ. Utah, 17 (No. 12):104, June, 1927. _Type._--Male adult, skin and skull; No. 44866, Museum of Vertebrate Zooelogy, University of California; Pine Canyon, 6,600 ft., 17 mi. NW Kelton, Box Elder County, Utah; July 12, 1930; collected by Annie M. Alexander; original number 676. _Range._--Mountainous regions of extreme northwestern Utah. _Diagnosis._--Size medium (see measurements). Color: Upper parts Buckthorn Brown grading over the sides and flanks to Light Buff on the underparts; chin white; nose and postauricular patches grayish black. Claws on front feet long and slender. Skull: Long and slender; rostrum long and narrow; zygomatic and mastoidal breadths slight; palatal pits deep; upper incisors narrow; basioccipital wide. _Comparisons._--Compared with topotypes of _Thomomys talpoides fisheri_, _gracilis_ is of approximately the same size. Upper parts darker and underparts lighter; postauricular patches larger and darker; claws on front feet longer and slenderer. Skull: Generally longer and narrower; nasals and rostrum longer; basioccipital wider. As compared with _T. t. uinta_, _gracilis_ is of approximately the same size but differs as follows: Color: Lighter throughout; postauricular patches markedly smaller and lighter; inguinal and pectoral regions much lighter. One characteristic difference is in the ear. In _uinta_ the external opening of the ear is much larger; the pinna of the ear is larger, more rounded at the tip, and lacks most of the pigmentation on the inner margin. Skull: Generally narrower and longer; nasals longer; zygomatic arches weaker and less angular; upper incisors narrower. This form is easily distinguished from _bridgeri_ by smaller size, and by the skull being longer, narrower and less angular. From _Thomomys talpoides oquirrhensis_ to the southeast, _T. t. gracilis_ can be distinguished by: Total length and ear shorter. Color: Generally lighter, except the underparts which are about the same; postauricular patches larger and more deeply pigmented. Skull: Braincase less inflated; nasals truncated posteriorly as opposed to rounded; zygomatic and mastoidal breadths less; rostrum shorter but narrower; upper incisors narrower and shorter. For comparisons with _wasatchensis_ see comparisons under that form. In general, this mountain form can be distinguished from all other _talpoides_ in Utah by lighter color, narrow, slender, "graceful" skull whence the name _gracilis_ is derived.