Part 4

Comparisons.--Compared with T. b. aureus, T. b. howelli differs as follows: paler; nasals shorter and wider; cranium more flattened; posterior extensions of premaxillae longer, thinner, and more acuminate.

Remarks.--T. b. howelli most closely resembles T. b. aureus; however, since only one adult specimen of T. b. howelli is known, it is impossible to appraise adequately its characters. Durrant (1952:211) records intergradation between T. b. howelli and T. b. osgoodi, and between T. b. howelli and T. b. aureus in Utah.

An attempt to collect specimens of T. b. howelli, in March, 1957, by Richard S. Miller and the writer was unsuccessful.

Specimens examined.--Total 2. Mesa Co.: Grand Junction, 4600 ft., 1 (USNM); Sieber Ranch, Little Doloris River, 1 (ERW).

=Thomomys bottae pervagus= Merriam

Thomomys aureus pervagus Merriam, Proc. Biol. Soc. Washington, 14:110, July 19, 1901; Cary, Proc. Biol. Soc. Washington, 20:26, March 27, 1907; Warren, Colorado College Publ., 33:77, January, 1908; Warren, Mammals of Colorado, p. 79, 1910, part; Cary, N. Amer. Fauna, 33:137, August 17, 1911, part.

Thomomys bottae pervagus, Goldman, Proc. Biol. Soc. Washington, 48:157, October 31, 1935.

Thomomys fulvus pervagus, Bailey, N. Amer. Fauna, 39:82, November 15, 1915.

Holotype.--Adult male, skin and skull, number 58293, United States National Museum, Espanola, Rio Arriba County, New Mexico, obtained by J. Alden Loring, January 4, 1894.

Distribution.--Upper Rio Grande and San Luis valleys of the Southern Rocky Mountains, in northern New Mexico and southern Colorado (see fig. 1).

Distinctive characters.--Yellowish Red (5YR 4/6); size large (see measurements); posterior tongues of premaxillae long, thin, and acuminate; nasals long, thin, posterior margins usually forming a wide V (see fig. 4); bullae rounded ventrally; interpterygoid space V-shaped, lacking median spicule.

Comparisons.--From T. b. aureus, T. b. pervagus differs as follows: reddish, never yellowish or blackish; posterior tongues of premaxillae thin and not deeply serrated; posterior margins of nasals forming a shallow V; interpterygoid space V-shaped, lacking a median spicule; basioccipital narrow. For comparisons with T. b. internatus, T. b. cultellus, and T. b. rubidus, see accounts of those subspecies.

Remarks.--T. b. pervagus is a well-defined subspecies. There is little variation between the topotypes and specimens from Colorado.

Specimens examined.--Total 20. Colorado: Conejos Co.: Antonito, 5 (USNM); 7 mi. E Antonito, 2 (USNM); 12 mi. E Antonito, 1 (USNM); Conejos River, 6 mi. W Antonito, 8300 ft., 2 (USNM). New Mexico: Rio Arriba Co.: Espanola, 10 (USNM).

=Thomomys bottae internatus= Goldman

Thomomys bottae internatus Goldman, Jour. Washington Acad. Sci., 26:115, March 15, 1936; Warren, Mammals of Colorado, p. 160, 1942; Kelson, Univ. Kansas Publ., Mus. Nat. Hist., 5:63, October 1, 1951.

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.

Variation is slight in the large series of topotypes of T. b. internatus. Specimens from other localities in the western part of the range differ little from the topotypes. Specimens from one mile west of Coaldale have slightly more inflated bullae that are more flattened ventrally. Specimens from five miles south of Cotopaxi also have the bullae more flattened ventrally.

Specimens from localities bordering the plains differ from the topotypes and near topotypes, and in general show greater variation from locality to locality. Specimens from 12 miles north of Canyon City are dark, resembling T. b. rubidus, but cranially agree with specimens from near Colorado Springs in being indistinguishable from specimens from Salida. Specimens from St. Charles Mesa and Bear Creek near Walsenburg differ from the topotypes in having wider rostra. The specimens from St. Charles Mesa have more inflated bullae.