_Specimens examined._--Total 93. Chaffee Co.: 2 mi. NNW Salida, 7100 ft., 3; _Salida_, 28 (20 ERW, 8 USNM). Fremont Co.: 12 mi. N Cañon City, 5; 1 mi. W Coaldale, 8; _Cotopaxi_, 1 (CSU); _5 mi. S Cotopaxi_, 12. El Paso Co.: 1-1/4 mi. S Colorado Springs, 2; _9 mi. SSW Colorado Springs_, 2; _17 mi. S Colorado Springs_, 1. Custer Co.: 2-1/2 mi. S Wetmore, 3; Santa Fe Drive and 20th Lane, Blende, 1; St. Charles Mesa, 5600 ft., 2 (CSU); Fork of Huerfano and Cucharas rivers, 2 (CMNH). Huerfano Co.: 11 mi. WNW Gardner, 7000 ft., 3; Gardner, 7000 ft., 2 (USNM); 1-1/2 mi. S Redwing, 3; Bear Creek, near Walsenburg, 2 (CSU); 1 mi. E La Veta, 8; 5 mi. SE La Veta, 2. =Thomomys bottae cultellus= Kelson _Thomomys bottae cultellus_ Kelson, Univ. Kansas Publ., Mus. Nat. Hist., 5:64, October 1, 1951. _Thomomys fulvus_, Cary, Proc. Biol. Soc. Washington, 20:26, March 27, 1907; Warren, Colorado College Publ., 33:76, January, 1908; Warren, Mammals of Colorado, p. 80, 1910. _Thomomys fulvus fulvus_, Bailey, N. Amer. Fauna, 39:80, November 15, 1915. _Holotype._--Adult male, skin and skull, number 70919, United States National Museum, Halls Peak, Mora County, New Mexico; January 13, 1895, obtained by C. Barber. _Distribution._--Raton Section of the Great Plains in northern New Mexico and extreme southern Colorado (see fig. 1). _Distinctive characters._--Dark (topotypes); size medium (see measurements); posterior tongues of premaxillae short; posterior margins of nasals forming a V (see fig. 5). _Comparisons._--From _T. b. pervagus_, topotypes of _T. b. cultellus_ differ as follows: darker, not so reddish; smaller; skull smaller; zygomatic arches relatively longer; bullae proportionately smaller and less inflated; basioccipital proportionately wider; posterior tongues of premaxillae shorter. Topotypes of _T. b. cultellus_ most closely resemble those of _T. b. internatus_ but differ as follows: darker; zygomatic arches more widely spreading, not so nearly parallel; nasals not so wide; bullae slightly more inflated. For a comparison with _T. b. rubidus_ see the account of that subspecies. _Remarks._--Kelson (1951:64) named _T. b. cultellus_ on the basis of six dark specimens (Dark Reddish Brown 5YR 3/4 and 2/2). Nowhere else within the range of this subspecies, as defined by Kelson, do any specimens resemble the topotypes in color. After comparing topotypes of _T. b. cultellus_ with topotypes of _T. b. internatus_ of approximately equal age, I disagree with Kelson (_loc. cit._) on some of the characters which he used to separate _cultellus_ from _internatus_. My findings indicate that _T. b. cultellus_ is not smaller, that its skull is not smaller and not less angular, and that the tympanic bullae are not less pointed ventrally. Further collecting is needed better to limit and diagnose this subspecies.