_Specimens examined._--Total 228. _Colorado_: LARIMER CO.: 6 mi. W, 1/2 mi. S Loveland, 5200 ft., 18; 3 _mi. N Loveland_, 3; _Loveland_, 4 (USBS). MORGAN CO.: 4 mi. W Orchard, 4 (Mich); _Orchard_, 1 (Mich). BOULDER CO.: Boulder, 91 (USNM 19, UC 12, Chi 60 examined, additional specimens in the collection); _Valmont_, 4 (UC). CLEAR CREEK CO.: Clear Creek, N side of Idaho Springs, 1. JEFFERSON CO.: Olivet, 10 (Denv). ADAMS CO.: Crook's Lake, 8 (Denv); Barr, 16 (Denv 15, ERW 1). ARAPAHOE CO.: Denver, 21 (USBS 3, AMNH 8, Denv 10). PARK CO.: William's Ranch, near Tarryall, 11 (Denv). TELLER CO.: Divide, 2 (ERW). EL PASO CO.: Colorado Springs, 31 (ERW 22, AMNH 7, MVZ 2); 12 mi. S Colorado Springs, 3 (MVZ). Microtus pennsylvanicus finitus new subspecies _Type._--Adult female, skin and skull, number 50204, University of Kansas, Museum of Natural History, obtained by J. K. Jones, Jr., original number 906, 5 miles north and 2 miles west of Parks in Dundy County, Nebraska, on August 16, 1952. _Range._--The valley of the north fork of the Republican River in eastern Colorado and southwestern Nebraska. _Diagnosis._--Entire animal and skull large; color dark for the species; zygomatic breadth large; upper molars large and upper molar tooth-row relatively long; braincase elongate; auditory meatus relatively small; bullae large; incisors relatively procumbent. _Comparisons._--From _M. p. uligocola_, the subspecies to the west, _M. p. finitus_ differs in darker color. These subspecies resemble each other in large size and large molar teeth. A comparison of nine pairs of skulls by the "method of pairs" shows three features in which _finitus_ (from at, or near, the type locality) differs from _uligocola_ (from at, or near, the type locality); in 7 of 9 pairs _finitus_ had a relatively more elongate braincase (Confidence Limit .60); in 9 of 9 pairs _uligocola_ had larger auditory meatuses (C. L. .99); in 7 of 9 pairs _uligocola_ had relatively larger bullae (C. L. .80). From _M. p. pennsylvanicus_ (Ord) from eastern Nebraska and eastern South Dakota _finitus_ differs in larger size; darker color; larger molar teeth and longer upper molar tooth-row. Five pairs of skulls were compared; in all 5 pairs, _finitus_ had more procumbent incisor teeth (C. L. .97) and wider first upper molars (C. L. .97); and in 4 of 5 pairs _finitus_ had a relatively more elongate braincase (C. L. .60). From _M. p. insperatus_, the subspecies to the north, _finitus_ differs as follows: color darker, size larger, molar teeth relatively larger and alveolar length of the upper molar tooth-row greater. Five pairs of skulls were compared and in all 5 pairs _finitus_ had more procumbent upper incisors (C. L. .97) than _insperatus_; in 4 of 5 pairs _insperatus_ had a relatively more elongate braincase (C. L.