. Bulletin - United States National Museum. Speciation and Dispersal The emarginatus group.—Present patterns of species distributionin the emarginatus group are insular and appear to have been greatlyinfluenced by extrinsic barriers to dispersal. Specific ranges arerestricted to valleys floored with cavernous limestone and separatedby ridges of insoluble, noncalcareous bedrock. Geographic distribu-tion of species and their proposed phylogenies are shown on the mapin figure 31 and by the dendogram in figure 32, respectively. The overall distribution of species in the emarginatus group is tosome
. Bulletin - United States National Museum. Speciation and Dispersal The emarginatus group.—Present patterns of species distributionin the emarginatus group are insular and appear to have been greatlyinfluenced by extrinsic barriers to dispersal. Specific ranges arerestricted to valleys floored with cavernous limestone and separatedby ridges of insoluble, noncalcareous bedrock. Geographic distribu-tion of species and their proposed phylogenies are shown on the mapin figure 31 and by the dendogram in figure 32, respectively. The overall distribution of species in the emarginatus group is tosome extent a reflection of the distribution of ancestral species. SUBTERRANEAN AJVIPHIPOD STYGONECTES 133 While present patterns of distribution readily correlate with the north-east-southwest linear orientation of valleys and ridges of the centralAppalachians, they are not otherwise easily interpreted in terms ofancestral dispersal. Migration of subterranean, ancestral stockinto the central Appalachians at a time when this area was reduced. Figure 31.—Distribution of species of Stygonedes in the central Appalachians. [Theemarginatus group: ® S. cooperi; A S. conradi; O S. emargiyiatus; O -S- gracilifes;-\-S. morrisoni; ? S. mundus; X S. stellmacki. The spinatus group: A S. symbols in a circle indicate two species from the same locality.] 134 NATIONAL MUSEUM BULLETIN 2 59 M 3 *• O ._ O JC u « (U •o Gl o o co
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