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.

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, ♀.

Fig. 3. Thomomys b. howelli, holotype, Grand Junction, 4600 ft., Mesa Co., Colorado. No. 75684 USNM, ♀.

Fig. 4. Thomomys b. pervagus, Espanola, 5000 ft., Rio Arriba Co., New Mexico. No. 133614 USNM, ♀.

Fig. 5. Thomomys b. cultellus, Fishers Peak, 8000 ft., Las Animas Co., Colorado. No. 129285 USNM, ♀.

Fig. 6. Thomomys b. internatus, Salida, 7050 ft., Chaffee Co., Colorado. No. 2757 ERW, ♀.

Fig. 7. Thomomys b. rubidus, holotype, 2-9/10 mi. E Cañon City, Fremont Co., Colorado. No. 72954, ♀.

Thomomys bottae rubidus new subspecies

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.

SUMMARY

A study of 249 specimens of Thomomys bottae from Colorado reveals six subspecies in the state. T. b. aureus and T. b. howelli occupy the Colorado Plateau Region in the western and southwestern parts of the state. T. b. internatus, T. b. cultellus, T. b. pervagus, and the newly named T. b. rubidus occupy part of the Southern Rocky Mountain Region and a narrow strip of the Great Plains.

The greatest amount of geographic variation, in Thomomys bottae in Colorado, occurs in the ecotone between the grassland and coniferous forest at the edge of the Great Plains, and in the ecotone between the Piñon, juniper, and sage of the Colorado Plateau and the Coniferous forest of the southern Rocky mountains.

Table 1. Measurements, in Millimeters, of Thomomys bottae

Unless otherwise noted, specimens are adults from Colorado