Thomomys perpallidus aureus Bailey, N. Amer. Fauna, 39:75, November 15, 1915; Barnes, Bull. Univ. Utah, 12 (No. 15):85, April, 1922; Bull. Univ. Utah, 17 (No. 12):100, June, 1927.
Type.—Male, adult skin and skull, No. 161654. U. S. National Museum (Biological Surveys Collection); Pine Valley Mountains, 5 mi. E Pine Valley, 8,300 ft., Washington County, Utah; April 10, 1909; collected by Clarence Birdseye; original number 861 (after Goldman, type not seen).
Range.—High mountains and plateaus of southwestern Utah.
Diagnosis.—Size medium (see measurements). Color: Upper parts between Cinnamon and Sayal Brown, finely mixed with black in median dorsal region, grading over sides and flanks to Cinnamon on underparts; front feet, hind feet, and distal part of tail white; postauricular patches, chin, cheeks and top of head grayish black. Skull: Depressed along median line of frontals and posterior ends of nasals; region of nasofrontal suture concave ventrally; zygomatic arches heavy and widely spreading, widest posteriorly; posterior ends of nasals straight, tending to be somewhat rounded in some specimens; extension of premaxillae posterior to nasals moderate; tympanic bullae moderately inflated ventrally; basioccipital wide; interpterygoid space widely V-shaped.
Comparisons.—Topotypes of birdseyei differ from near topotypes of Thomomys bottae virgineus, from Beaverdam Wash as follows: Size larger; tail and hind foot longer. Color: Darker throughout, between Cinnamon and Sayal Brown as opposed to Cinnamon Buff. Skull: Larger in every measurement taken except extension of premaxillae posterior to nasals, and length and width of rostrum which are less; skull more depressed in nasofrontal region; zygomatic arches more widely spreading; zygomatic processes of squamosals shorter; pterygoid hamulae longer; tympanic bullae smaller and less inflated ventrally.
Among named races of T. bottae, birdseyei most closely resembles trumbullensis in size, but differs as follows: Hind foot and tail longer. Color: Lighter throughout; postauricular patches smaller and lighter. Skull: Larger; mastoid breadth less; zygomatic arches wider and more widely spreading posteriorly; median frontal depression more marked; extension of premaxillae posterior to nasals greater; tympanic bullae less inflated ventrally; molariform teeth larger.
For comparisons with Thomomys bottae planirostris see account of that form.
Remarks.—T. b. birdseyei is apparently endemic to the mountainous area of southwestern Utah in Washington and Iron counties. It intergrades with virgineus and with planirostris as described in the account of the latter.
Specimens examined.—Total, 8, distributed as follows: Washington County: Pine Valley, 1 (U. S. N. M.); Pine Valley Mountains, 5 mi. E Pine Valley, 8,300 ft., 3 (U. S. N. M.); Pine Valley campground, 6,800 ft., 1 (R. H.); 3/4 mi. E town of Pine Valley, 6,500 ft., 3 (R. H.).
Additional records.—Washington County: Hebron, 1; Mountain Meadows, 2 (Bailey 1915:75).