Thomomys aureus pervagus, Warren, Mammals of Colorado, p. 80, 1910, part; Cary, N. Amer. Fauna, 33:137, August 17, 1911, part.
Thomomys fulvus pervagus, Bailey, N. Amer. Fauna, 39:82, November 15, 1915, part.
Holotype.—Adult male, skin and skull, number 150997, United States National Museum, obtained at Salida, 7000 feet, Chaffee County, Colorado, by Merritt Cary, November 10, 1907.
Distribution.—Southern Rocky Mountain Province; southwestern part of the Colorado Piedmont, and Raton Section of the Great Plains, to the east of the Sangre De Cristo Range (see fig. 1).
Distinctive characters.—Yellowish Red (5YR 5/6.5); size medium (see measurements); posterior tongues of premaxillae short; posterior margins of nasals forming a V (see fig. 6); bullae pointed ventrally; interpterygoid space V-shaped, lacking a median spicule; basioccipital narrow.
Comparisons.—From T. b. pervagus, topotypes of T. b. internatus differ as follows: uniformly paler, not so reddish; smaller; skull smaller; posterior tongues of premaxillae shorter; bullae smaller, less inflated, and more pointed ventrally; zygomata less angular.
For comparisons with T. b. cultellus and T. b. rubidus, see accounts of those subspecies.
Remarks.—The dividing line between T. b. internatus and T. b. cultellus is drawn arbitrarily since only one specimen has been collected between La Veta Pass and the border of New Mexico.
When Goldman (1936:115) named T. b. internatus he included specimens from Union and Colfax counties, New Mexico, and specimens from Gardner, Colorado (not Garfield as stated by Kelson, 1951:66). The specimens from New Mexico and a specimen from Fishers Peak, Colorado, were subsequently assigned to T. b. cultellus by Kelson (loc. cit.).
The specimen from Fishers Peak shows some characters that might be interpreted as intermediate between internatus and cultellus, but shows also some unique characters that can be understood only by further collecting in the regions north and northeast of the type locality of T. b. cultellus.