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.