Bailey (N. Amer. Fauna, 39:73, November 15, 1915) assigned a series of 7 specimens from Lone Willow Spring, California, to the subspecies _Thomomys bottae perpes_. This locality lies at the northern edge of the Mohave Desert. Later, Grinnell (Univ. California Publ. Zool., 17:427, April 25, 1918) named the pocket gophers from approximately the eastern half of the Mohave Desert, _Thomomys perpallidus_ [= _bottae_] _mohavensis_, but failed to mention the specimens recorded by Bailey, and thus their subspecific identity is in doubt. We find that _T. b. mohavensis_ differs from _T. b. perpes_ in more pallid color (light yellowish as opposed to dark rufescent) larger size, larger and more angular skull, angular (as opposed to more evenly bowed) zygomatic arches, larger and deeper audital bullae, narrower interpterygoid space, and proportionately greater mastoidal breadth. In external measurements, size and angularity of skull, width of interpterygoid space and angularity of the zygomatic arch, the specimens from Lone Willow Spring seem to be intermediate between the two subspecies, but perhaps show more resemblance to _T. b. mohavensis_. Otherwise, the specimens closely resemble _T. b. mohavensis_ to which they are here referred. The specimens provide a northern marginal record of occurrence for that subspecies.
Other specimens recorded as _T. b. perpes_ by Bailey (_loc. cit._) from Grapevine Ranch, California, have also not been mentioned in later publications although, from a geographic standpoint, they might be better referred to either _Thomomys bottae pascalis_ or _T. b. mohavensis_. Comparison of specimens of _T. b. mohavensis_ and _T. b. pascalis_ from various localities show _T. b. pascalis_ to be larger (including the skull), darker, and to possess a more nearly vertical occipital plane, wider-spread but less angular zygomatic arches, less inflated tympanic bullae, wider braincase (which consequently appears to be less inflated), proportionately longer and slenderer rostrum, and broader nasals distally. Cranially, _T. b. pascalis_ differs from _T. b. perpes_ in essentially the same ways, but to an event greater degree. In color, _T. b. pascalis_ differs from _T. b. perpes_ in being duller, less rufescent.