Part 3

Specimens examined.--Total, 993, distributed as follows: All specimens unless otherwise indicated are in the University of Kansas Museum of Natural History. Specimens in other museums are labeled as follows: Chicago Natural History Museum (Chi); University of Michigan, Museum of Zoology (Mich); American Museum of Natural History (AMNH); United States National Museum (USNM); Biological Surveys Collection (USBS). Localities that are not represented in Fig. 1 because overlapping or crowding of the symbols would result are Italicized. Localities are arranged from north to south by states, within a state from northwest to southeast by counties, and within a county from north to south.

WYOMING: Yellowstone Park: Canyon Camp, 1 (USBS); Lower Geyser Basin, 1 (USBS); Upper Yellowstone River, 2 (AMNH); North end of Lake, Yellowstone National Park, 2 (AMNH). Teton Co.: Pacific Creek, 1 (USBS); Big Game Ridge, 3 (USBS 1, Mich 2); Whetstone Creek, 7 (Mich); Moran and environs (6 localities within a 5 mile radius), 28 (USBS 2, Mich 5); S fork Buffalo River, 7 (AMNH); 2 mi. W pass, Black Rock Creek, 1 (USBS); Jenny Lake, 5 (Mich); Bar BC Ranch, 2-1/2 mi. NE Moose, 6500 ft., 2; Teton Pass above Fish Creek, 1 (USBS); Jackson and environs, 142 (Mich 141); Sheep Creek, 2 (Mich). Lincoln Co.: 13 mi. N, 2 mi. W Afton, 2; 10 mi. N, 2 mi. W Afton, 4; 9-1/2 mi. N, 2 mi. W Afton, 3; 9 mi. N, 2 mi. W Afton, 9; 7 mi. N, 1 mi. W Afton, 12; Afton, 1 (USBS); Labarge Creek, 1 (USBS); Border, 6 (USBS); Cokeville, 2 (USBS); 6 mi. N, 2 mi. E Sage, 1; Cumberland, 5 (USBS). Sublette Co.: 34 mi. N, 4 mi. W Pinedale, 1; 33 mi. N, 2 mi. W Pinedale, 6; 32 mi. N, 1 mi. W Pinedale, 1; 31 mi. N Pinedale, 4; Dell Creek, on Ferris Ranch, 7 (Mich); Horse Creek, 7800 ft., Merna, 4 (USBS); Big Piney, 1 (USBS). Fremont Co.: 17-1/2 mi. W, 2-1/2 mi. N Lander, 9500 ft., 3; 17 mi. W, 2 mi. N Lander, 9300 ft., 4; Milford and environs (5 localities within a 1 mile radius), 23 (USBS 4); 15-1/2 mi. S, 7-1/2 mi. W Lander, 9200 ft., 1; South Pass City, 8000 ft, 8 (USBS); 23-1/2 mi. S, 5 mi. W Lander, 8600 ft., 7. Natrona Co.: Deer Creek, 16 mi. S, 11 mi. W Waltman, 6950 ft., 44; 6 mi. S, 2 mi. W Casper, 5900 ft., 4; 6-4/5 mi. S, 2 mi. W Casper, 6100 ft., 1; 7 mi. S, 2 mi. W Casper, 6370 ft., 3; 10 mi. S Casper, 7750 ft., 33; Sun, 2 (USBS); 5 mi. W Independence Rock, 6000 ft., 4; 5 mi. W, 1 mi. S Independence Rock, 2. Converse Co.: Beaver, 1 (USBS). Uinta Co.: 1-1/2 mi. W, 1/2 mi. S Cumberland, 6; 16 mi. S, 2 mi. W Kemmerer, 6700 ft., 3; 10 mi. SW Granger, 3 (Mich); Fort Bridger, 6650 ft., 25 (USNM 6); 9 mi. S Robertson, 8000 ft., 9; 9-1/2 mi. S, 1/2 mi. W Robertson, 8600 ft., 1; 10 mi. S, 1 mi. W Robertson, 8700 ft., 25; 14 mi. S, 2 mi. E Robertson, 9000 ft., 5; 4 mi. S Lonetree, 1 (USBS). Sweetwater Co.: Farson, 3; Bitter Creek, 3 (AMNH); Kinney Ranch, 21 mi. S Bitter Creek, 6800 ft., 9 (USNM 1, AMNH 2); 32 mi. S, 22 mi. E Rock Springs, 7025 ft., on Vermillion Creek, 15. Carbon Co.: 18 mi. NNE Sinclair, 6500 ft., 10; Bridgers Pass, 18 mi. SW Rawlins, 7500 ft., 7; Saratoga, 1 (USBS); 6 mi. S, 13 mi. E Saratoga, 8500 ft., 5; 6 mi. S, 14 mi. E Saratoga, 8800 ft., 1; Lake Marie, 10,440 ft., 2; 1 mi. S Lake Marie, 2; 1/2 mi. S, 2 mi. E Medicine Bow Peak, 10,800 ft., 1; Encampment (12 localities from 10 mi. N, 14 mi. E to 9 mi. N, 3 mi. E Encampment and from 6500 to 8400 ft.), 63; 1/4 mi. N Riverside, 7380 ft., 2; S base Bridger Peak, 8800 ft., Sierra Madre Mountains, 1; 2 mi. S Bridger Peak, 9300 ft., 2; Savery (10 localities from 8 mi. N, 21 mi. E to 4 mi. N, 8 mi. E Savery and from 7300 to 8800 ft.), 80. Albany Co.: 30 mi. N, 10 mi. E Laramie, 6760 ft., 6; 29-3/4 mi. N, 9-1/2 mi. E Laramie, 6350 ft., 1; 26 mi. N, 4-1/2 mi. E Laramie, 6960 ft., 8; 26-3/4 mi. N, 6-1/2 mi. E Laramie, 6700 ft., 3; 3 mi. N, 13 mi. E Laramie, 7500 ft., 1; 7 mi. N, 2 mi. E Laramie, 1 (Chi); 5 mi. N Laramie, 7400 ft., 15; Laramie, 4 (AMNH); 1 mi. E Laramie, 7160 ft., 4; 7-7/10 mi. SSW Laramie, 7200 ft., 4; 6-1/2 mi. S, 8-3/4 mi. E Laramie, 8200 ft., 1; Headquarters Park, 10,200 ft., Medicine Bow Mountains, 3 (USBS); Centennial, 8120 ft., 1; 2-1/4 mi. ESE Brown's Peak, 10,300 ft., 3; 3 mi. ESE Brown's Peak, 10,000 ft., 12; 2 mi. S Brown's Peak, 10,600 ft., 1; Pole Mountain, 15 mi. SE Laramie, 4 (USBS 3); 1 mi. SSE Pole Mountain, 8350 ft., 4; 2 mi. SW Pole Mountain, 8300 ft., 13; 3 mi. S Pole Mountain, 8100 ft., 1; Sherman, 2 (AMNH). Laramie Co.: 5 mi. N, 1 mi. W Horse Creek P. O., 7200 ft., 1; Meadow, 2 (USBS); 11 mi. N, 5-1/2 mi. E Cheyenne, 5450 ft., 7; 7 mi. W Cheyenne, 6500 ft., 10; Cheyenne, 3 (USNM).

COLORADO: Moffat Co.: Lay, 6160 ft., 1 (AMNH). Routt Co.: Wright's Ranch, Yampa, 7700 ft., 2; Gore Range, 8 mi. E Toponas, 8000 ft., 2 (USBS). Larimer Co.: 12-1/2 mi. W, 1-1/2 mi. S Rustic, 1; 11 mi. W, 1 mi. S Rustic, 1; Cache La Poudre River, 1 (Chi); Estes Park, 3 (USBS 1, AMNH 2); 19-1/2 mi. W, 2-1/2 mi. S Loveland, 7280 ft., 6; 16 mi. W Loveland, 6840 ft., 1; 6 mi. W, 1/2 mi. S Loveland, 5200 ft., 1. Rio Blanco Co.: Meeker, 1 (USBS); 9-1/2 mi. SW Pagoda Peak, 7700 ft., 3; 5 mi. S Pagoda Peak, 9100 ft., 2. Eagle Co.: Eagle, 1 (USBS); Pando, 2 (USBS). Grand Co.: Mt. Whiteley, 2 (USBS); Arapahoe Pass, Rabbit Ear Mountains, 2 (USBS); Coulter (near Granby), 5 (USBS); Arrowhead (near Dale), 1 (USBS). Boulder Co.: 3/4 mi. N, 2 mi. W Allenspark, 8400 ft., 4; 3 mi. S Ward, 9000 ft., 3; Nederland, 16 (Chi). Clear Creek Co.: Mt. McLellan, 2 (USBS); Berthoud Pass, 4. Park Co.: Trout Creek Ranch, 2 mi. N Garo, 1 (USBS).

Specimens examined of M. m. nanus from eastern Idaho and Montana are as follows: IDAHO: Custer Co.: Challis, 7 (USBS); Mill Creek, Challis Nat. Forest, 1 (USBS); Pahsimeroi Mts., 12 (USBS); Lost River Mts., 1 (USBS). Fremont Co.: N fork Snake River, 10 mi. SW Island Park, 6200 ft., 2 (AMNH); Black Springs Creek, 4 mi. W Ashton, 5200 ft., 1 (AMNH); 5 mi. W St. Anthony, 5000 ft., 1 (AMNH). Camas Co.: Camas Prairie, Corral, 5100 ft., 2 (USBS). Blaine Co.: Alturas Lake, 3 (USBS); Sawtooth Lake, 2 (USBS); Craters of the Moon, Laidlow Park, 2 (Mich); Ticura, 10 mi. S Picabo, 1 (USBS); 19 mi. NE Carey (Lava Lake), 8 (Mich). Butte Co.: 26 mi. SW Arco, 12 (Mich). Bingham Co.: Shelley, 6 (USBS). Bonneville Co.: 10 mi. SE Irwin, 4 (USBS). Owyhee Co.: Three Creeks, 3 (USBS). Twin Falls Co.: Castleford Fenced Plot, 11 mi. W, 9 mi. S Twin Falls, 1. Minidoka Co.: Heyburn, 2 (USBS). Cassia Co.: 2 mi. S, 2 mi. W Burley, 5. Bannock Co.: Pocatello, 23 (USBS 4); Swan Lake, 1 (USBS). Bear Lake Co.: Montpelier Creek, 6700 ft., 3 (USBS). MONTANA: Gallatin Co.: W. Fork of W. Fork, Gallatin River, 1 (USBS). Park Co.: Lamar River, 7000 ft., 1 (USBS); Gardiner, 1 (USBS). Sweet Grass Co.: 14 mi. S Big Timber, 1 (USBS); McLeod, 1 (USBS); West Boulder Creek, 18 mi. SE Livingston, 2 (USBS).

=Microtus montanus codiensis=, new subspecies

Type.--Female, adult, skin and skull; No. 27578, Museum of Natural History, University of Kansas, from 3-1/5 mi. E and 3/5 mi. S Cody, 5020 ft., Park Co., Wyoming; obtained on August 11, 1948, by James W. Bee, original number 18-8-11-48.

Range.--In northwestern Wyoming eastward from the Absaroka and Wind River ranges into the western part of the Big Horn Basin.

Diagnosis.--A relatively large Microtus montanus; tail actually and relatively long; hind foot actually but not relatively large; skull large; zygomatic expanse actually and relatively large; alveolobasilar length relatively large; upper molar tooth-row relatively long; color relatively light, not reddish.

Guide to subspecies

1. M. m. nanus 2. M. m. codiensis 3. M. m. zygomaticus 4. M. m. fusus 5. M. m. micropus 6. M. m. nexus 7. M. m. amosus 8. M. m. rivularis ]

Comparisons.--As compared with the specimens of M. m. nanus from Idaho, the size is larger (see diagnosis and measurements). Certain proportions which differ from those of nanus and which are not in close agreement with the observed differences with age in specimens of nanus of a size comparable to codiensis are relatively large alveolobasilar length, relatively long alveolar length of upper molar tooth-row, relatively wide-spreading zygomatic arches, and relatively long tail. The color in codiensis is lighter than in nanus. As compared to the new subspecies named below from the Big Horn Mountains to the east, codiensis is of similar size in head-body length, but has a relatively as well as actually longer tail; the hind foot averages longer; the upper molar tooth-row is relatively longer; the color is slightly paler and less grizzled; the bullae are larger and less flattened; the angle formed at the suture between the basioccipital and basisphenoid bones is less acute; and the region of the suture is less prominently elevated between the bullae when viewed from the ventral aspect. The pterygoid plates mesial and posterodorsal to the posterior end of the last upper molar are less fenestrated, and the incisive foramina are less constricted posteriorly.

Measurements.--The average and the extremes for some measurements of 34 males and females, 27 from the type locality and 7 from other localities in the range assigned to this subspecies, are as follows: total length, 165 (146-186); length of tail, 44.2 (35-55); hind foot, 19.6 (17-21); condylobasilar length of the skull, 25.5 (24.0-27.5); zygomatic breadth, 15.6 (14.7-16.6); alveolar length of upper molar tooth-row, 6.6 (6.2-7.0); prelambdoidal breadth, 8.8 (8.1-9.5); lambdoidal breadth, 12.0 (11.2-12.8). As an indication of variability and for comparison with other series the coefficient of variability and two times the standard error of the mean for each measurement in this series are included in Table 1. The averages for some measurements of 27 topotypes are as follows: total length, 162; length of tail, 45.5; hind foot, 19.9; condylobasilar length, 25.6; palatilar length, 14.0; molar series, 6.6; alveolobasilar length, 14.9; zygomatic breadth, 15.6; interorbital breadth, 3.5; lambdoidal breadth, 12.1; prelambdoidal breadth, 8.9; depth of braincase, 7.8.

Discussion.--Three species of Microtus were collected by James W. Bee at the type locality. Microtus montanus codiensis, Microtus longicaudus mordax, and Microtus pennsylvanicus modestus were taken in the same runways in the same meadow, at the same time. Microtus ochrogaster haydeni, although not taken at this locality, occurs in the Big Horn Basin. These four species differ in their geographic ranges, being largely allopatric, except M. montanus and M. longicaudus which are sympatric. Although the different species have ecological preferences and habits which differ, several species of Microtus may occur together in local areas such as the above. Certain of the characteristics of M. m. codiensis are intermediate between those of the species M. montanus on one hand and those of the other three species on the other hand. Could interspecific hybridization between "good species" of Microtus take place in nature and possibly alter the characteristics of a local population?

Specimens examined.--Total, 50, distributed as follows (abbreviations for collections are given in the account of M. m. nanus; localities that are not represented in Fig. 1 because overlapping or crowding of the symbols would result are Italicized):

MONTANA: Carbon Co.: Beartooth Mountains, 2 (USBS); Beartooth Lake, 1 (USBS).

WYOMING: Park Co.: Black Mountain, head of Pat O'Hara Creek, 3 (USBS); 13 mi. N, 1 mi. E Cody, 5200 ft., 1; SW slope Whirlwind Peak, 9000 ft., 1; 5 mi. N Cody, 6300 ft., 1 (USBS); 3-1/5 mi. E, 3/5 mi. S Cody, 31; Ishawooa Creek, 6300 ft., 2 (USBS); Valley, 1 (USBS); Needle Mountain, 10,500 ft., 4 (USBS). Hot Springs Co.: 3 mi. N, 10 mi. W Thermopolis, 4950 ft., 3.

=Microtus montanus zygomaticus=, new subspecies

Type.--Male, adult, skin and skull, No. 32761, Museum of Natural History, University of Kansas, from Medicine Wheel Ranch, 9000 ft., 28 mi. E Lovell, Big Horn County, Wyoming; obtained by R. Freiburg, original number 105.

Range.--The Big Horn Mountains of north-central Wyoming.

Diagnosis.--A large Microtus montanus with a relatively short tail; short molar series; broad zygomatic arches well rounded in lateral outline when viewed from above; small and flattened bullae; raised basioccipito-basisphenoid suture.

Comparisons.--For comparison with M. m. codiensis from the west, on the other side of the Big Horn Basin, see the account of that subspecies. In comparison with nanus this subspecies is slightly paler, in this respect showing more resemblance to codiensis although not so pale, and more grizzled or unevenly colored. This difference in color between zygomaticus and codiensis may not be of taxonomic significance. From both the topotypes of nanus, and the series of it from Wyoming, zygomaticus differs on the average in having a relatively shorter tail, a relatively shorter upper molar tooth-row, relatively more rounded and relatively more wide-spread zygomatic arches, and smaller more flattened bullae.

Measurements.--Average and extreme measurements of 24 adult males and females from several localities here referred to M. m. zygomaticus are as follows: total length, 159(150-175); length of tail, 37.6(31-46); hind foot, 18.6(17-20); condylobasilar length of the skull, 25.3(24.2-26.7); zygomatic breadth, 15.3(14.1-16.7); alveolar length of upper molar tooth-row, 6.2 (5.7-6.8); prelambdoidal breadth, 8.7(8.3-9.4); lambdoidal breadth, 11.9(11.0-12.5). Average and extreme measurements of a series of 12 adult male topotypes are as follows: total length, 159(144-174); length of tail, 36.4 (30-41); hind foot, 18.2(16-20); condylobasilar length of skull, 25.8(24.7-26.7); alveolobasilar length, 14.8(13.8-15.3); palatilar length, 13.8 (12.7-14.2); alveolar length of upper molar tooth-row, 6.4(5.9-6.6); zygomatic breadth, 15.9 (15.0-16.7); interorbital breadth, 3.6(3.4-3.7); lambdoidal breadth, 12.1 (11.5-12.5); prelambdoidal breadth, 8.6(8.3-8.9); depth of braincase, 8.0 (7.6-8.3).

Discussion.--This subspecies is separated from M. m. codiensis to the west by the Big Horn Basin. A series from along Buffalo Creek, 27 mi. N, 1 mi. E Powder River, 6075 ft., in Natrona County, Wyoming, is intermediate between the topotypes of zygomaticus and nanus in the characters cited above as distinguishing the two, but shows greater resemblance to zygomaticus in the shape of the zygomatic arch, in color which is paler than in topotypes of zygomaticus, and in the short hind foot. On these and on geographic grounds this population is referred to zygomaticus. Unfortunately we cannot be certain in many cases that an intermediate condition in a certain character indicates a genetically intermediate population and therefore true intergradation between the two subspecies to which the population is geographically intermediate. The topotypes of this subspecies are the most distinct of all the series which I have studied from the eastern Rocky Mountains, in terms of the degree of morphological departure from the norm for the species. After zygomaticus the following populations are arranged according to their degree of deviation from this norm (codiensis deviates most): topotypes of codiensis, fusus and a population from southern Sweetwater County, Wyoming, and lastly the nanus-caryi complex. Within the latter group, as I have mentioned, there are a number of local variants most of which do not differ significantly and do not conform to any geographic pattern.

Specimens examined.--Total, 55, distributed as follows (abbreviations for collections are given in the account of M. m. nanus; localities that are not represented in Fig. 1 because overlapping or crowding of the symbols would result are Italicized): WYOMING: Big Horn Co.: Medicine Wheel Ranch, 9000 ft., 28 mi. E Lovell, 30; W slope, head of Trappers Creek, 9500 ft., 2 (USBS). Washakie Co.: 9 mi. E, 5 mi. N Tensleep, 7400 ft., 1. Johnson Co.: 7-1/2 mi. W, 1 mi. S Buffalo, 6500 ft., 3; Big Horn Mountains, 3 (USBS). Natrona Co.: Buffalo Creek, 27 mi. N, 1 mi. E Powder River, 6075 ft., 16.

=Microtus montanus fusus= Hall

Microtus nanus, Bailey, N. Amer. Fauna, 17:30, June 6, 1900 (part); Cary, N. Amer. Fauna 33:123, August 17, 1911.

Microtus montanus fusus Hall, Proc. Biol. Soc. Washington, 51:131-134, August 23, 1938; Warren, The Mammals of Colorado, Univ. of Okla. Press, p. 229, 1942.

Type.--Male, adult, skin and skull; No. 61281, Museum of Vertebrate Zoology; 2-1/2 miles east of summit of Cochetopa Pass, Saguache County, Colorado; Sept. 21, 1933; collected by Annie M. Alexander; original number 2568. Type not seen by me.