The variability in color is relatively greater in topotypes of both uligocola and of modestus than in many of the other series studied. Specimens from Denver and Colorado Springs taken in late autumn and winter (October to February) are paler, more reddish and less blackish, than specimens taken in June and July at Loveland. This reddishness results from longer, and more intensely reddish tips of the hair. The entire hairs also are longer. The average weight of 16 adults (12 males and 4 non-pregnant females) from near Loveland is 49.7 gms. The average length of the ear is 13.4.

Specimens examined.—Total 228. Colorado: Larimer Co.: 6 mi. W, ½ 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. .60), narrower first upper molariform tooth (C. L. .75), and shorter distance between the alveoli of the first upper molars (C. L. .88).

Remarks.—The species, Microtus pennsylvanicus, in Pleistocene time ranged onto the plains of Kansas as far southward as Meade County, Kansas (Hibbard, 1940:421). This occurrence indicates a cooler more humid climate then than now in southwestern Kansas. M. p. finitus is more closely associated with water than Microtus ochrogaster, the only other species of Microtus now occupying the same region, although both species have been captured at certain places in the same runways. In Nebraska, a marginal part of the range of the species, M. pennsylvanicus has been taken at scattered localities. This scattered and localized distribution of suitable habitat undoubtedly limits gene-flow between these relict populations. Presumably as a result of this isolation finitus has accumulated and maintained its distinctive characteristics. The subspecies is so named because of its limited range. The average weight of eight specimens (4 males and 4 non-pregnant females) from Dundy County is 57.2 grams.

Specimens examined.—Total 26. Colorado: Yuma Co.: Wray, 3 (USBS); 1 mi. W Laird, 2. Nebraska: Dundy Co.: 5 mi. N, 2 mi. W Parks (Rock Creek State Fish Hatchery), 19; Haigler, 2 (USBS).

Microtus pennsylvanicus pullatus new subspecies