Six specimens (21249-21253, 212706 BS) from Rice, Arizona, were referred by Goldman (Proc. Biol. Soc. Washington, 46:76, April 27, 1933) to the subspecies Thomomys bottae mutabilis Goldman when he proposed that name as new, but these six specimens were not mentioned by him when he later named Thomomys bottae alienus (Jour. Washington Acad. Sci., 28:338, July 15, 1938), to which subspecies the specimens in question might be expected to belong. Examination of the six specimens reveals that they are intergrades between T. b. mutabilis and T. b. alienus but that the specimens more closely resemble the latter. More precisely, slightly larger size of skull, greater ventral inflation of tympanic bullae, and less depressed occipital region ally the specimens with Thomomys bottae alienus, and we identify them as that subspecies. The two subspecies concerned are not so distinct as are most subspecies of Thomomys bottae.
Thomomys bottae aphrastus Elliott
Bailey (N. Amer. Fauna, 39:58, November 15, 1915) referred three specimens from San Antonio, Baja California, to Thomomys bottae nigricans. These specimens have not, to our knowledge, been re-examined subsequently, although the current taxonomic treatment of the pocket gophers of Baja California by Huey (Trans. San Diego Soc. Nat. Hist., 10(4):245-268, 1 map, August 31, 1945) excludes T. b. nigricans from the area of San Antonio. The pertinent specimens are probably Nos. 10810-10812 in the Chicago Natural History Museum. We have examined the specimens and, using the comparative materials listed under the account of T. b. siccovallis, find them to be intermediate in most characters between T. b. aphrastus and T. b. martirensis. Because they more nearly resemble T. b. aphrastus in the weakly-spreading zygomatic arches, we refer the specimens from San Antonio to that subspecies.
Thomomys bottae jojobae Huey
When Huey (Trans. San Diego Soc. Nat. Hist., 10:256, August 31, 1945) named Thomomys bottae jojobae from Sangre de Cristo, Baja California, México, he made no mention of a specimen that Bailey (N. Amer. Fauna, 39:58, November 15, 1915) identified as Thomomys bottae nigricans from La Huerta, which place is approximately eight miles northwest of Sangre de Cristo. From a geographic standpoint, it seemed unlikely that the specimen from La Huerta would be referable to T. b. nigricans. Examination of the specimen (138752 BS) proves it to differ from topotypes of T. b. nigricans and to agree with T. b. jojobae in richer, more rufescent color, especially ventrally, and smaller, slenderer, more delicate skull. The specimen is therefore tentatively referred to Thomomys bottae jojobae. We have not, however, compared it with specimens of Thomomys bottae juarezensis, a subspecies the range of which lies to the east on the summit of the Sierra Juárez.
Thomomys bottae martirensis J. A. Allen
Bailey (N. Amer. Fauna, 39:58, November 15, 1915) referred pocket gophers from Piñon on the west slope of the San Pedro Mártir 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 Piñon (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.
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.