. The Canadian field-naturalist. 3 m. m Figure L Epimeral plates 1-3 of richmon- densis. 10 12 14 16 18 Length (mm) Figure 2. Length curves of three populations of Crangonyx richmondensis. contrast, Amherst specimens had lengths of to mm and to mm for females and males, respectively, which is intermediate between both subspecies. Figure 2 illustrates combined values for each sex. Substantial variation occurs among local populations as demonstrated by inconsistencies in discussed characters. The Sunderland popula- tion contains apical spine counts, suggesting C. r.
. The Canadian field-naturalist. 3 m. m Figure L Epimeral plates 1-3 of richmon- densis. 10 12 14 16 18 Length (mm) Figure 2. Length curves of three populations of Crangonyx richmondensis. contrast, Amherst specimens had lengths of to mm and to mm for females and males, respectively, which is intermediate between both subspecies. Figure 2 illustrates combined values for each sex. Substantial variation occurs among local populations as demonstrated by inconsistencies in discussed characters. The Sunderland popula- tion contains apical spine counts, suggesting C. r. richmondensis, but length ranges that imply C. r. laurentianus. The reverse prevails in the Amherst population. Leverett animals generally tend toward C. r. laurentianus in all characters. These results agree with Bell's (1971) analysis of Vermont specimens. Although he "provisionally" assigned the material to C. r. laurentianus, his examined specimens had length features of C. r. laurentianus and apical spine counts of C r. richtnondensis. It therefore seems unwise to consider the west-central New England forms as belonging to either subspecies. The zone of intergradation between both sub- species is then extended eastward from central New York (Holsinger 1972) to include west- central New England (Figure 3). This wide gap between seemingly good subspecies may rep- resent a non-clinal continuum resulting from mixing of two differentiated forms reinvading formerly glaciated areas (see Historical Zoo- geography section). Historical Zoogeography It is beyond the scope of this paper to recount the history of the genus in eastern North America. The occurrence of two seem-. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Ottawa Field-Naturalists' Club. Ottawa, Ottawa Field-Naturalists' Club
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