Type.—Male, adult, skin and skull, No. 43980, Museum of Vertebrate Zoölogy, University of California; Fehlman Ranch, 3 mi. N Kelton, 4,225 ft., Box Elder County, Utah; September 27, 1929; collected by Louise Kellogg; original number 451.
Range.—Northwestern Utah, and extreme western Utah as far south as the southern end of the Deep Creek Mountains.
Diagnosis.—Size medium (see measurements); claws on front feet small. Color: Near Cinnamon on dorsal and ventral surfaces; inguinal region, front and hind feet and distal third to half of tail white; nose, cheeks and postauricular patches grayish black. Skull: Moderately angular and ridged; zygomatic arches nearly parallel with sides of skull; jugals vertical; marked thickening at union of jugal and zygomatic process of maxilla; greatest zygomatic breadth at anterior part of arches; interpterygoid space lyre-shaped; ventral margin of jugal concave dorsally; nasals long and denticulate distally; parietal ridges bowed in at two places, at coronal suture and at middle of interparietal; paroccipital processes extremely well developed; dorsal frontomaxillary suture usually straight.
Comparisons.—From near topotypes of Thomomys bottae centralis, aureiventris differs as follows: Size larger; tail shorter; hind foot longer; claws on front feet shorter. Color: Slightly darker on upper parts, but with greater extension of white on ventral surface. Skull: Zygomatic breadth greater; greatest width across zygomatic arches at anterior rather than posterior region; zygomatic arches thicker at union of jugals and zygomatic processes of maxillae; dorsal frontomaxillary suture less convex medially; mastoid breadth greater; extension of premaxillae posterior to nasals less; interpterygoid space lyre-shaped rather than V-shaped.
From topotypes of Thomomys bottae albicaudatus, aureiventris can be distinguished by: Size larger; hind foot longer. Color: Markedly lighter throughout, Cinnamon as opposed to near (13''''n) Black. Skull: Larger in all but three measurements taken; extension of premaxillae posterior to nasals less; alveolar length of upper molar series shorter; zygomatic arches widest anteriorly rather than posteriorly; thickening at union of jugal and zygomatic process of maxilla markedly greater; interpterygoid space lyre-shaped as opposed to V-shaped; lacrimal processes more globose at tips.
Thomomys bottae aureiventris can be readily distinguished from T. b. bonnevillei, sevieri, wahwahensis, and convexus by larger size in all measurements taken and darker coloration. The same differences obtain in comparison with T. b. tivius and stansburyi except that aureiventris is much lighter colored. See comparisons under those forms.
Remarks.—T. b. aureiventris has one of the most extensive ranges of any race of T. bottae occurring in Utah. The range extends from the valleys of the northwest corner of the state south along the extreme western margin of the state approximately to the southern end of the Deep Creek Mountains. This ascribed range practically bounds the northwest and western margins of the great salt desert in Box Elder and Tooele counties. As far as known, this great waste area harbors no members of the Geomyidae. Pocket gophers were available from four localities in addition to the type locality. In these four localities all of the animals were intergrades. The three specimens from Queen of Sheba Canyon, Deep Creek Mountains, although smaller than aureiventris in every measurement taken, resemble it in color and general configuration of the skull. The animals from Trout Creek and Ibapah at the southern end of the range, although referred to aureiventris, are intermediate between it and centralis. In color and measurements they more closely resemble centralis, but the skulls closely resemble those of aureiventris. The skulls show some slight characteristics of bonnevillei, the form to the east, which indicate an early relationship between the two. Specimens from the east side of Tecoma Range, adjacent to Pilot Peak, although referred to aureiventris are intergrades between it and centralis. Although this locality is nearer the type locality of aureiventris than any of the other record stations, the animals show the maximum departure from topotypes in morphological features. In color they approach centralis, and agree with it in one-half of the measured characters. The general configuration of the skull and a majority of the critical diagnostic characters, for example, jugal thickening, are more nearly as in aureiventris. From the above remarks it is readily understood that this subspecies is extremely variable.
Specimens examined.—Total, 55, distributed as follows: Box Elder County: Fehlman Ranch, 3 mi. N Kelton, 4,255 ft., 8 (7, M. V. Z.); Utah-Nevada Boundary, E Side Tecoma Range, 4,300 ft., 12. Tooele County: Ibapah, 5,000 ft., 21. Juab County: Queen of Sheba Canyon, W side Deep Creek Mountains, 5,600 ft., 11.
Thomomys bottae robustus new subspecies
Type.—Male, adult, skin and skull, No. 2726, Museum of Zoölogy, University of Utah; Orr's Ranch, Skull Valley, 4,300 ft., Tooele County, Utah; June 19, 1938; collected by S. D. Durrant; original number 1583.