. The Canadian field-naturalist. 260 The Canadian Field-Naturalist Vol. 91 subsequent isolation of ice-formed, water-filled depressions and kettle holes, C. r. richmon- densis found refuge, surviving in those areas able to maintain low water temperatures and other environmental requirements, including avoid- ance of excessive siltation and in-filling. The known localities for C. richmondensis in south- central New England lie outside the influence of heavy sedimentation typical of larger, tempo- rary glacial lakes. Crangonyx r. richmondensis eventually migrated north of the Appalachian divide.
. The Canadian field-naturalist. 260 The Canadian Field-Naturalist Vol. 91 subsequent isolation of ice-formed, water-filled depressions and kettle holes, C. r. richmon- densis found refuge, surviving in those areas able to maintain low water temperatures and other environmental requirements, including avoid- ance of excessive siltation and in-filling. The known localities for C. richmondensis in south- central New England lie outside the influence of heavy sedimentation typical of larger, tempo- rary glacial lakes. Crangonyx r. richmondensis eventually migrated north of the Appalachian divide. Northwesterly migration brought C r. richmondensis in contact in valley areas with C. r. laurentianus migrating northeasterly from Mississippian refugia. This mixing resulted in interbreeding among populations of each sub- species, thus creating the observed wide band of variability that presently exists (Figure 3). During the latter stages of glacial recession C. pseudogracilis followed the same northerly route along the Atlantic coast as was suggested. Figure 3. Proposed tracks utilized by the eastern glacial isolate Crangonyx richmondensis richmodensis during postglacial dispersal. Shaded area depicts zone of intergradation of both species. Map key: D = Delaware River, H = Hudson River, C = Con- necticut River, M = Mohawk River, LO = Lake Ontario, LC = Lake Champlain; dashed line = Ter- minal moraine of Pleistocene glaciation, solid line = Appalachian Divide, arrows = direction of dis- persal, 18000 shoreline during maximum glaciation follows Curray (1965).. 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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