_Comparisons._--For comparisons of _virgineus_ with _Thomomys bottae planirostris_ and _T. b. birdseyei_ see accounts under those forms.
Topotypical specimens of _virgineus_ can be distinguished from those of _Thomomys bottae trumbullensis_ as follows: Size smaller. Color: Lighter throughout. Skull: Zygomatic arches less widely spreading; jugals more bowed medially; zygomatic processes of squamosals longer; extension of premaxillae posterior to nasals greater; tympanic bullae larger and more inflated ventrally; molariform teeth larger.
Compared with topotypes of _Thomomys bottae centralis_, _virgineus_ differs in: Size smaller; tail shorter; hind foot smaller. Color: Deeper Cinnamon Buff, thus darker in overall appearance. Skull: Smaller, but relatively wider; zygomatic processes of maxillae heavier; region of maxillo-jugal sutures thicker; jugals more concave laterally; tympanic bullae more inflated ventrally; molariform teeth larger.
_Remarks._--This pocket gopher occupies practically the same range in Utah as the large kangaroo rat _Dipodomys deserti deserti_ Stephens. Both are found in the Beaverdam Wash. The type locality of _virgineus_ is but a short distance down the Beaverdam Creek at Littlefield, Arizona. It intergrades with _birdseyei_, the mountain form to the north and east (see remarks under _birdseyei_). There are evidences of intergradation with _planirostris_ of the Virgin River Valley above the narrows of the Virgin River where it cuts through the Beaverdam Mountains (see the discussion under _planirostris_). There are intergradational tendencies exhibited towards _centralis_ in some specimens. Some of the animals are practically indistinguishable in color and there are intergrading cranial characters in the nasals, zygomatic arches and tympanic bullae.
_Specimens examined._--Total, 20, distributed as follows: _Washington County_: Beaverdam Wash, 8 mi. N Utah-Arizona border, 7; Beaverdam Wash, 5 mi. N Utah-Arizona border, 2,600 ft., 13.
_Thomomys perpallidus planirostris_ Burt, Proc. Biol. Soc. Washington, 44:38, May 8, 1931.
_Thomomys bottae planirostris_ Hall and Davis, Proc. Biol. Soc. Washington, 47:52, February 9, 1934; Goldman, Proc. Biol. Soc. Washington, 48:156, October 31, 1935; Presnall, Zion-Bryce Mus. Bull., 2:14, January, 1938; Long, Journ. Mamm., 21:176, May 14, 1940.