Sydney Anderson

“ In some characteristics of the skulls, populations within Pennsylvania differed as much or more than the subspecies from Wyoming and Colorado. In other characteristics of the skulls and of the skins differences are greater between populations in Wyoming and Colorado. ”

“ Variation with age is important to the taxonomist even among specimens designated as "adults", because growth and changes in various proportions continue throughout the life of the mice. The possibility that differences detected in the statistical treatment or observed directly could be the result of differences in average age within the samples of "adults" was considered in each case.
In order to study certain variations, the following "method of pairs" was used. Skulls of two series to be compared were matched in pairs so that they corresponded in size and ontogenetic stage of development. ”

“ Furthermore the geographic variation in one feature may be only partly correlated with the variation in another feature. The variation in M. p. pullatus is an example: Specimens from near Pocatello, Idaho, are darker than topotypes of modestus but specimens from Fremont County, Idaho, are indistinguishable from topotypes of modestus (Davis, 1939:315) . I have examined a number of mice from the Bitterroot Valley in western Montana and the color value for 12 adults is 2.7. They are slightly but not significantly paler than topotypes of modestus. ”

“ 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. ”

“ A single skin (KU 42407, from 11⁄2 miles east of Buckhorn in Weston County, Wyoming) was selected as a representative of the paler mice and arbitrarily given the number 2. A single skin (KU 17491, from 3 miles east of Moran in Teton County, Wyoming) was selected as a representative of the darker mice from the western part of Wyoming and arbitrarily given the number 4. These mice were selected so that they were respectively paler and darker than the estimated average of the total variation within the populations to be studied, but the two mice were not at the extremes of paleness and darkness. ”

“ Specimens in other museums are designated beyond as follows: American Museum of Natural History (AMNH) ; Museum of Zoology, University of Michigan (Mich) ; Chicago Natural History Museum (Chi) ; United States National Museum (USNM) ; Biological Surveys Collection (USBS) ; Museum of Vertebrate Zoology, Berkeley, California (MVZ) ; Colorado Museum of Natural History, Denver (Denv) ; E. R. Warren collection, Colorado College, Colorado Springs (ERW) ; University of Colorado Museum, Boulder (UC) .
ACCOUNTS OF SUBSPECIES
Microtus pennsylvanicus modestus (Baird) ”

“ 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 ”

“ Geographic variation in color in Microtus pennsylvanicus in the Rocky Mountains. Paler colors are represented by smaller numbers. Numbers are derived from the series of specimens listed in the text by the method described there. The subspecies that occur in the region studied are as follows:
For each of the series listed in Table 1 all adult mice having skulls that measured more than 24.0 mm. ”