_Specimens examined._--Total 130. _Colorado_: CHAFFEE CO.: Salida, 3 (ERW). SAGUACHE CO.: Monshower Meadows, 27 mi. NW Saguache [=3 mi. E Cochetopa Pass], 8 (USBS); _Tevebaugh's Ranch, 20 mi. W Saguache_, 46 (USBS, there are additional specimens not examined in detail by me); _Cochetopa Pass, 33 mi. W Saguache_, 1; 3 mi. N, 16 mi. W Saguache, 8500 ft., 5; 5 mi. NW Hooper, 1 (AMNH); Medano Ranch, 15 mi. NE Mosca, 2 (1 ERW, 1 USBS). CUSTER CO.: Westcliffe, 7800 ft., 1 (ERW). ALAMOSA CO.: _Hooper_, 10 (2 AMNH, 8 Denv); _Mosca_, 3 (ERW). CONEJOS CO.: 1-1/2 mi. E Manassa, 11. COSTILLA CO.: Alamosa, 3 (Mich); 2 mi. S Blanca, 7800 ft., 6 (MVZ). _New Mexico_: TAOS CO.: Arroyo Hondo, 7600 ft., 6 (USBS); Taos, Pueblo, 1 (USNM). COLFAX CO.: 1 mi. S, 2 mi. E Eagle Nest, 8100 ft., 21; Taos Mountains, east slope, 8800 ft., 1 (USBS); _Coyote Creek_, 1 (USBS). Microtus pennsylvanicus uligocola new subspecies _Type._--Adult male, skin and skull, number 26898, University of Kansas, Museum of Natural History, obtained by James O. Lounquist, original number 349, 6 miles west and 1/2 mile south of Loveland, 5200 ft., Larimer Co., Colorado, on July 26, 1948. _Range._--Northern Colorado. See Figure 2 and list of specimens examined. _Diagnosis._--Entire animal and skull large; color average for the species, neither extremely pale or dark in summer pelage; molar tooth-row long; nasals narrow; maxillary septum large; first upper molar wide; anterior margin of zygomatic arch above infraorbital foramen not deeply indented; fenestrae in posterodorsal parts of squamosal bones relatively long; braincase not elongate; auditory bullae and meatus large.