Thomomys bottae albicaudatus Hall
Thomomys perpallidus albicaudatus Hall, Univ. California Publ. Zoöl., 32:444, July 8, 1930; Univ. California Publ. Zoöl., 37:3, April 10, 1931.
Thomomys bottae albicaudatus Goldman, Proc. Biol. Soc. Washington, 48:156, October 31, 1935; Durrant, Bull. Univ. Utah, 28 (No. 4):5, August 18, 1937.
Thomomys perpallidus aureiventris Hall, Univ. California Publ. Zoöl., 37:3, April 10, 1931.
Type.—Male, adult, skin and skull, No. 43971, Museum of Vertebrate Zoölogy, University of California; Provo, 4,510 ft., Utah County, Utah; October 17, 1929; collected by Annie M. Alexander; original number 506.
Range.—From the area between the Great Salt Lake and the Wasatch Mountains south along the western margin of the central mountains of the state to the Sevier River, in Juab County, west into Tooele County to the Onaqui and Sheeprock mountains.
Diagnosis.—Size medium (see measurements); claws on front feet medium. Color: Upper parts near (13''''n) Black, grading over sides and flanks to Pinkish Cinnamon on underparts; chin, nose, top of head and postauricular patches black; front feet, hind feet and distal third to half of tail white. Skull: Angular and ridged; zygomatic arches moderately wide spreading, widest posteriorly; paroccipital processes weak; zygomatic processes of maxillae convex anteriorly; lacrimal processes small and peglike; jugals convex dorsally on ventral surface; nasals short, rounded distally and truncate proximally; parietal crests bowed in, in two places; interpterygoid space broadly V-shaped.
Comparisons.-For comparisons of albicaudatus with Thomomys bottae aureiventris and centralis see accounts of those forms.
Topotypes of albicaudatus are dark colored and can be distinguished from those of Thomomys bottae birdseyei, tivius, stansburyi and contractus which are also dark forms, by larger size and larger, more robust skulls (see accounts of those forms). It can be distinguished from the remainder of the known subspecies of Thomomys bottae in Utah by darker color and by cranial details (see accounts of those forms).
Remarks.—The range of albicaudatus is larger than that of any other race of Thomomys bottae limited to Utah. Specimens are available from thirty localities which represent widely varied habitats and environments. This subspecies consists of many highly variable local populations, and the marginal populations intergrade freely with adjacent races. In many populations, it is really difficult to recognize the relationships on account of the great variation, and one is frequently tempted to name some of them as distinct. Careful study of the large number of specimens has enabled me to recognize diagnostic characters common to all of these variable populations. The animals range from large and dark at the north to small and light at the south.