. The Canadian field-naturalist. 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).. Figure 4. Proposed track utilized by the east
. The Canadian field-naturalist. 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).. Figure 4. Proposed track utilized by the eastern glacial isolate Crangonyx pseudogracilis during postglacial dispersal. See Figure 3 for map key. Shaded area depicts known present distribution of the species in study area. for the two crayfish Orconectes limosus (Raf.) and Procambarus a. acutus (Harland) by Ortmann (1906) and Crocker (1957) (Figure 4). Dispersal probably was controlled by flooding processes in coastal zones correlated with a rising sea-level. A review of the ecology of C. pseudogracilis in this study and in Bousfield (1958) shows that this species is a lowland river and pond inhabitant. Observations discussed earlier indicate an annual shoreward migration in spring. Animals massing in shallows near river mouths during spring floods could move between drainage basins. Adventives of C. pseudogracilis most likely entered the southern Connecticut coastal plain during glacial Lake Hitchcock times, in the period following the Middletown re-advance about 13000 Between the time of glacial lake formation and final draining about 10700 (Schafer and Hartshorn 1965; Hartshorn 1969) C. pseudogracilis s^ntdLdnorih- ward through the temporarily common Quinnipiac-Farmington valley lake-drainage system (Lougee 1938) as indicated by the presence of a relict population (E. Mills collection). Further eastward, the species entered the Connecticut Valley 'and passed northward through the New Britain spillway into Lak
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