_Thomomys fossor moorei_ Goldman, Journ. Washington Acad. Sci., 28:335, July 15, 1938. _Thomomys talpoides moorei_ Goldman, Journ. Mamm., 20:234, May 14, 1939. _Type._--Male, adult, skin and skull, No. 248222, U. S. National Museum (Biological Surveys Collection); 1 mi. S Fairview, 6,000 ft., Sanpete County, Utah; February 19, 1928; collected by A. W. Moore; X-catalogue number 24799 (after Goldman, type not seen). _Range._--Wasatch Plateau in Sanpete, Utah, Carbon and Emery counties, and in Wasatch Mountains south of Spanish Fork Canyon. _Diagnosis._--Size medium (see measurements). Color: Upper parts between Cinnamon and Sayal Brown, with mixture of black hairs, grading through Cinnamon on sides and flanks to Pale Pinkish Buff on underparts, clearest on inguinal and pectoral regions; nose and cheeks dusky; postauricular patches medium in size and black; ears black; chin buffy white; front and hind feet white; tail mostly white with brownish hairs on dorsal surface. Skull: Large, robust; nasals long and deeply emarginate on posterior ends, and dilated distally; zygomatic arches robust and widely spreading; zygomatic processes of maxillae heavy; interparietal comparatively small, but always wider than long; extension of premaxillae posterior to nasals short; tympanic bullae moderate in size, but markedly inflated ventrally; pterygoid hamulae long; interpterygoid space narrowly V-shaped; upper incisors long and moderately recurved; molariform teeth light. _Comparisons._--Topotypes of _moorei_ differ from topotypes and near topotypes of _Thomomys talpoides uinta_ as follows: Size slightly larger. Color: Upper parts and sides lighter; tail lighter; postauricular patches larger and darker; ears more pointed, smaller and darker. Skull: Larger, heavier and more massive; nasals longer, but deeply emarginate posteriorly as in _uinta_; rostrum wider and longer; zygomatic arches heavier and more angular; zygomatic processes of maxillae heavier; interparietal generally smaller and shorter; braincase wider; tympanic bullae more inflated ventrally; interpterygoid space more narrowly V-shaped; upper incisors longer, but not as procumbent; molariform teeth smaller. Topotypes of _moorei_ can be distinguished from those of _Thomomys talpoides oquirrhensis_ as follows: Size slightly larger; tail longer; ears larger, less pointed. Color: Lighter throughout; postauricular patches larger. Skull: More ridged and angular; nasals narrower posteriorly, but more dilated distally; posterior ends of nasals more deeply emarginate (while shallowly emarginate in _oquirrhensis_, they tend to be somewhat rounded); rostrum narrower; extension of premaxillae posterior to nasals greater; least interorbital breadth less; zygomatic arches more angular and widely spreading; zygomatic processes of maxillae heavier; interparietal smaller; tympanic bullae larger and more inflated ventrally; upper incisors generally longer.