. The Canadian field-naturalist. 350 The Canadian Field-Naturalist Vol. 96 species in the field in southwestern British Columbia. All these characters have their limitations as dis- criminators. Hennings' and Hoffmann's tooth charac- ter for example is difficult or impossible to use in old adults with heavily worn teeth. Moreover in some areas of British Columbia, on Vancouver Island, the tooth pigmentation is very pale and reduced in some specimens. Tail length and color likewise have their limitations. It is true that in areas of sympatry in British Columbia the larger long-tailed subsp
. The Canadian field-naturalist. 350 The Canadian Field-Naturalist Vol. 96 species in the field in southwestern British Columbia. All these characters have their limitations as dis- criminators. Hennings' and Hoffmann's tooth charac- ter for example is difficult or impossible to use in old adults with heavily worn teeth. Moreover in some areas of British Columbia, on Vancouver Island, the tooth pigmentation is very pale and reduced in some specimens. Tail length and color likewise have their limitations. It is true that in areas of sympatry in British Columbia the larger long-tailed subspecies of 5". monticolus can usually be distinguished from the smaller short-tailed S. vagrans with a certain degree of probability. A comparison of tail lengths of S. m. isolatus and S. v vancouverensis from Vancouver Island, and S. m. setosus and s. v. vagrans from the mainland of southwestern British Columbia revealed a probability of misidentification in the range of to I, or approximately one wrong identification out of 9 to 13 (van Zyll de Jong, unpublished data). Farther to the east in British Columbia, where S. v. vagrans converges with the smaller shorter-tailed S. m. obscurus, the probability of misidentification using tail length increases to approximately , or one out of three incorrect identifications. It is obvious that the use of an additional morphological character to identify these two species would be desirable. While examining samples of S. monticolus and S. vagrans from southern British Columbia in the collec- tion of the National Museum of Natural Sciences, I found that the toes of 5. monticolus are relatively longer and possess a greater number of small paired digital callosities or friction pads than those of S. vagrans. This is especially evident in the toes of the hind feet (Figure 1). In S. monticolus there are five or six paired friction pads on the second to fourth digit. In S. vagrans the number never exceeds four. This character i
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