Type.—Female, adult, skin and skull; No. 27578, Museum of Natural History, University of Kansas, from 3⅕ mi. E and ⅗ 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
- M. m. nanus
- M. m. codiensis
- M. m. zygomaticus
- M. m. fusus
- M. m. micropus
- M. m. nexus
- M. m. amosus
- M. m. rivularis
- M. m. nanus
- M. m. codiensis
- M. m. zygomaticus
- M. m. fusus
- M. m. micropus
- M. m. nexus
- M. m. amosus
- 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.