The ranges of Pleurocera (formerly Goniobasis or Elimia) catenaria (Say, 1822) and P. proxima (Say, 1825) extend from Virginia south through the Carolinas into the piedmont and upper coastal plain of Georgia, where they intersect with populations of P. floridensis (Reeve, 1860). In contrast to the situation in surrounding states, however, Georgia populations of P. catenaria have been taxonomically subdivided and re-described under at least ten specific nomina, over a complex monographic history extending 150 years. To see if this increased nomenclatural diversity might signal higher levels of population divergence, we compared gene frequencies at 11 polymorphic allozyme-encoding loci among eight populations of P. catenaria and three populations of P. floridensis sampled from central Georgia region to three populations of P. proxima, which have never been taxonomically subdivided. Genetic variation was moderate within our 14 populations and high among them, as has been reported in many prior surveys of pleurocerid allozyme divergence conducted elsewhere. The pairwise genetic distances demonstrated among our populations of P. catenaria from Georgia were lower than those observed among control P. proxima populations, or among a comparable sample of P. catenaria populations from the Carolinas previously published. Central Georgia does not appear to be a region of pleurocerid endemicity, but rather of faunal suturing, the proliferation of specific nomina attributable to qualitatively higher levels of shell morphological variation, possibly ecophenotypic in origin. Junior synonyms of P. catenaria include albanyensis, boykiniana, caelatura, darwini, mutabilis, postelli, suturalis and viennaensis. Junior synonyms of P. floridensis include inclinans, induta, exul, and nymphaea. The Goodrich nomen timidus is retained as a subspecies of P. floridensis (new combination). We suggest that faunas demonstrating great evolutionary stasis, such as the pleurocerid populations of central Georgia, might profitably serve as the next “laboratories of speciation.”
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