_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.). =Thomomys bottae nesophilus= Durrant _Thomomys bottae nesophilus_ Durrant, Bull. Univ. Utah, 27 (No. 2):2, October, 1936; Marshall, Journ. Mamm., 21:156, May 14, 1940. _Type._--Male, adult, skin and skull, No. 1136, Museum of Zooelogy, University of Utah; Antelope Island, Great Salt Lake, Davis County, Utah; April 20, 1935; collected by S. D. Durrant; original number 761.