As far as known, _T. b. muralis_ is completely isolated from other populations of pocket gophers by uninhabitable eroding cliffs. The animals have been found only on isolated terraces in the lower end of Prospect Valley (itself a lateral pocket) within the Grand Canyon of the Colorado River, Hualpai Indian Reservation, Arizona. Consequently it is unlikely that intergradation with other populations could exist at the present time. In short, in arranging _muralis_ as a subspecies of _Thomomys bottae_, we are influenced, not by the demonstration of intergradation, but by the degree of morphological differentiation of the population and the probable reasons therefor. ~Thomomys bottae mutabilis~ Goldman Goldman (Jour. Washington Acad. Sci., 28:342, July 15, 1938) named the subspecies _Thomomys bottae pinalensis_ on the basis of only one specimen, an immature female (245709 BS) from Oak Flat, five miles east of Superior, Pinal Mountains, Arizona. Examination shows it to be indistinguishable in characters of taxonomic importance (coloration, external measurements, shape of skull and size of skull) from specimens of _T. b. mutabilis_ of comparable sex and age. No. 245709 is well within the limits of individual variation of _T. b. mutabilis_ as is shown by the several specimens (all in the U. S. Biological Surveys Collection) as follow: Nos. 214118, 214670 (topotypes from Camp Verde, Arizona), 212707 (Chiricahua Ranch, 20 mi. E Calva), 208635 (H-bar Ranch, 20 mi. S Payson), and 215762 (Turkey Creek). Therefore, the name _Thomomys bottae pinalensis_ is here arranged as a synonym of the earlier name, _Thomomys bottae mutabilis_ Goldman (Proc. Biol. Soc. Washington, 46:75, April 27, 1933), the type locality of which is Camp Verde, Yavapai County, Arizona. ~Thomomys bottae patulus~ Goldman