_Specimens examined._--Total 13. _Colorado_: Las Animas Co.: Fishers Peak, about 8000 ft., 1 (USNM). _New Mexico_: Union Co.: Near Folsom, 4 (CMNH); Colfax Co.: Philmont Ranch, Cimarroncito, 8100 ft., 2. Mora Co.: Halls Peak, 6 (USNM). [Illustration: Figs. 2-7. Dorsal views of skulls of _Thomomys bottae_. × 1. Fig. 2. _Thomomys b. aureus_, 3 mi. W Durango, La Plata Co., Colorado. No. 72967, Female. Fig. 3. _Thomomys b. howelli_, holotype, Grand Junction, 4600 ft., Mesa Co., Colorado. No. 75684 USNM, Female. Fig. 4. _Thomomys b. pervagus_, Espanola, 5000 ft., Rio Arriba Co., New Mexico. No. 133614 USNM, Female. Fig. 5. _Thomomys b. cultellus_, Fishers Peak, 8000 ft., Las Animas Co., Colorado. No. 129285 USNM, Female. Fig. 6. _Thomomys b. internatus_, Salida, 7050 ft., Chaffee Co., Colorado. No. 2757 ERW, Female. Fig. 7. _Thomomys b. rubidus_, holotype, 2-9/10 mi. E Cañon City, Fremont Co., Colorado. No. 72954, Female.] =Thomomys bottae rubidus= new subspecies _Holotype._--Adult female, skin and skull, number 72954, Museum of Natural History, University of Kansas, trapped by Richard S. Miller and Phillip M. Youngman, original number 253 (PMY), 2-9/10 miles east of Cañon City, 5344 feet, Fremont County, Colorado, March 17, 1957. _Distribution._--Known only from Garden Park in Cañon City and from the type locality (see fig. 1). _Distinctive characters._--Dark (Reddish Brown 5YR 3/3); size large (see measurements); skull large; rostrum wide; zygomatic arches rounded and broadly spreading (see fig. 7); alveolar length of upper maxillary tooth-row small. _Comparisons._--From topotypes of _T. b. internatus_, _T. b. rubidus_ differs as follows: uniformly darker; skull averages larger in all measurements, except alveolar length of upper maxillary tooth-row, which is smaller; rostrum proportionately wider and tapered anteriorly; zygomatic arches more rounded; bullae more rounded in lateral view. Specimens of _T. b. rubidus_ differ from topotypes of _T. b. pervagus_ in darker color; rostrum wider posteriorly; posterior extensions of premaxillae shorter; bullae smaller, proportionately more inflated posteriorly; zygomatic arches more rounded; wider across squamosals; alveolar length of upper maxillary tooth-row greater. From topotypes of _T. b. cultellus_, _T. b. rubidus_ differs as follows: paler; larger in all measurements taken; rostrum proportionately wider; zygomatic arches more rounded, less angular; angle formed by zygomatic arch and rostrum greater; bullae proportionately smaller, not so pointed anteriorly; alveolar length of upper maxillary tooth-row shorter. _Remarks._--The range of _T. b. rubidus_ is surrounded by the range of _T. b. internatus_; nevertheless, intergradation has not been found. For a discussion of the geographic relation of _T. b. rubidus_ to _T. b. internatus_ see page 374.