Bailey (N. Amer. Fauna, 39:58, November 15, 1915) referred pocket gophers from Pinon on the west slope of the San Pedro Martir Mountains, Baja California, to the subspecies _Thomomys bottae nigricans_. The subspecific identity of these animals has now been reinvestigated subsequently, although the locality whence they were obtained is far removed from what is now thought to be the geographic range of _T. b. nigricans_; further, several other subspecies are known to occur in the intervening area. We have examined the available material from Pinon (13853-13855 BS) and find the specimens to agree with _Thomomys bottae martirensis_ and to differ from _T. b. nigricans_ in lighter color, larger, more ridged and angular skull; proportionately greater mastoidal breadth; narrower occipital shelf; more ventrally produced alveolar ramus of the maxillae; and deeply concave posterior border of the temporal root of the zygomatic arch. These specimens thus constitute the northernmost record of _T. b. martirensis_ known to us. ~Thomomys bottae mohavensis~ Grinnell 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.