Type.—Male, adult, skin and skull, No. 264805, U. S. National Museum (Biological Surveys Collection); Richfield, 5,308 ft., Sevier County, Utah; March 11, 1928; collected by A. W. Moore; X-catalogue number 28835 (after Goldman, type not seen).
Range.—Sevier River Valley from Piute County north to southwestern Juab and northeastern Millard counties, Utah.
Diagnosis.—Size large (see measurements). Color: Upper parts Cinnamon Buff mixed with black in middorsal region; sides, flanks, forearms, thighs and underparts Pinkish Buff; inguinal region, front feet, hind feet, underpart of tail and end of tail white; postauricular patches small and dusky; chin, cheeks, nose and top of head dusky. Skull: Largest of Utah gophers, massive and angular; nasals long and denticulate distally; rostrum long and relatively narrow; zygomatic arches widely spreading and heavy throughout; jugals nearly vertical; zygomatic processes of maxillae heavy and flaring out abruptly from base of rostrum; union of zygomatic process of maxilla and jugal greatly thickened; extension of premaxillae posterior to nasals long; posterior tongues of premaxillae relatively narrow; lacrimal processes small; pterygoid hamulae long; interpterygoid space moderately V-shaped, tending to be somewhat lyre-shaped in some specimens; tympanic bullae somewhat flattened, only moderately inflated ventrally; upper incisors long and narrow; molariform teeth actually large, but relatively small.
Comparisons.—Topotypes of lenis can be distinguished from those of Thomomys bottae tivius, convexus, contractus, albicaudatus, levidensis, centralis and aureiventris by the following markedly greater average measurements of males: Total length, 250 mm.; length of nasals, 15.5; zygomatic breadth, 28.3; mastoid breadth, 22.5; and length of rostrum, 18.3. Other distinguishing characters are: Zygomatic arches more widely spreading; length of zygomatic processes of maxillae greater; and relatively longer, narrower rostrum.
Remarks.—Twenty-one animals obtained from Lynndyl, Millard County, are all intergrades between lenis and aureiventris. They are like aureiventris in the shape of the zygomatic arches, and in the bowing of the parietal crests. Slight intergradation with centralis is indicated by color and the shape of the nasals. The transverse arching of the posterior part of the rostrum is indicative of some relationship with contractus. In six other characters studied they most closely approach lenis to which they are here referred.
Large size is the distinctive feature of Thomomys bottae lenis. The skulls are the largest of any species or subspecies of Thomomys found in Utah. In total length, however, these animals are no longer than the extremes found in other named races. When Goldman (1942:75) described this race as new, he referred it to the species Thomomys townsendii, but remarked that the animal from Richfield was different enough from any other form then named to merit probably full specific status. I know of no character other than size to separate Thomomys townsendii from Thomomys bottae, and since intergradation has been shown to exist between these alleged townsendii from Richfield and animals from extreme western Utah known to belong to the species bottae, lenis is here arranged as a subspecies of Thomomys bottae which name has priority over Geomys townsendii.
The range here ascribed to this race is the Sevier River Valley from Piute County as far downstream as the town of Lynndyl which is near the eastern mainland of Pleistocene Lake Bonneville. The Sevier River continues farther out into Delta Valley ultimately to empty into Sevier Lake, which at present is adjacent to the area that formerly constituted the western mainland of the aforementioned ancient lake. This watercourse may have provided a migration route in ancient times, during the fluctuations of Lake Bonneville, whereby the animals formerly of the western mainland were able to come far eastward. The animals from Lynndyl which are intergrades between lenis, an eastern mainland form, and centralis and aureiventris which are western mainland forms of Lake Bonneville lend support to this hypothesis.
Specimens examined.—Total, 26, distributed as follows: Millard County: Lynndyl, 4,796 ft., 21. Juab County: U. B. (= Yuba) Dam, 5,000 ft., 1. Sevier County: Salina, 4,575 ft., 1; Richfield, 5,308 ft., 3. (U. S. N. M.).
Thomomys bottae levidensis Goldman
Thomomys bottae levidensis Goldman, Proc. Biol. Soc. Washington, 55:76, June 25, 1942.