Thomomys bottae minimus Durrant, Proc. Biol. Soc. Washington, 52:161, October 11, 1939; Marshall, Journ. Mamm., 21:154, May 14, 1940.
Type.—Male, adult, skin and skull, No. 263942, U. S. National Museum (Biological Surveys Collection); Stansbury Island, Great Salt Lake, Tooele County, Utah; June 25, 1938; collected by William H. Marshall; original number 141.
Range.—Known only from the type locality.
Diagnosis.—Size small (see measurements); tail relatively long. Color: Upper parts Pinkish Buff, darker on head; underparts Pale Pinkish Buff; front and hind feet white; nose, chin and postauricular patches black. Skull: Long, slender and nearly devoid of ridges; braincase moderately inflated; interparietal quadrangular; zygomatic arches weak, widest in temporal region, but neither widely spreading nor angular; nasals straight and truncate posteriorly; extension of premaxillae posterior to nasals relatively great; tympanic bullae moderately inflated; palatal pits deep; rostrum short but narrow; interpterygoid space moderately lyre-shaped; upper incisors narrow; molars light.
Comparisons.—Compared with topotypes of Thomomys bottae albicaudatus, minimus differs as follows: Size markedly smaller; claws on front feet shorter and weaker. Color: Markedly lighter throughout, being Pinkish Buff as contrasted with near (13''''n) Black. Skull: Smaller in every measurement taken; slender, smooth, weak and nonangular as opposed to ridged, robust, wide and angular; zygomatic arches much weaker and not so widely spreading posteriorly; ascending processes of premaxillae much narrower; extension of premaxillae posterior to nasals less; interpterygoid space moderately lyre-shaped as opposed to V-shaped; dentition lighter.
Topotypes of minimus differ from those of Thomomys bottae aureiventris as follows: Size markedly smaller. Color: Lighter dorsally and no "gold color" on underparts. Skull: Markedly smaller in every measurement taken; weak, smooth and slender as opposed to ridged, angular and robust; zygomatic arches weak and widest posteriorly rather than heavy and widest anteriorly; no great thickening at region of union of jugal and zygomatic process of the maxilla; jugals more nearly straight rather than concave laterally; interpterygoid space not so markedly lyre-shaped; dentition lighter.
The races nearest geographically to minimus are Thomomys bottae nesophilus and T. b. stansburyi. For comparisons see accounts of those forms.
Remarks.—This subspecies is the smallest of all the races of Thomomys bottae occurring in Utah. As far as known it is endemic to Stansbury Island, and since the Pleistocene Lake Bonneville attained its highest level has remained on that part of Stansbury Island that was above this high level. (See comments under nesophilus.) The sandy nature of the soil and the desert conditions of the area that has since been exposed at lower levels apparently do not constitute a favorable environment. Unlike nesophilus from Antelope Island, this form does not have its affinities with albicaudatus, the valley form of the adjacent mainland, but does show affinities with stansburyi, the nearest mountain form on the mainland. This is easily understood when one realizes that Stansbury Island is only an isolated part of Stansbury Mountain that projects northward as a peninsula into Great Salt Lake. The history of Stansbury Island with reference to isolation of minimus parallels that of nesophilus on Antelope Island. See discussion under nesophilus.
Specimens examined.—Total, 5, as follows: Tooele County: Stansbury Island, Great Salt Lake, 5 (U. S. N. M.).