In this volume we report the results of the largest-scale inventory of freshwater snails ever conducted in the United States. We have reviewed and synthesized macrobenthic collections taken by ten natural resource agencies, malacological holdings at eight museums, and our own original collections from hundreds of sites, covering all freshwater gastropod habitat in Atlantic drainage systems from Georgia to the New York state line. Information theoretical analysis of the 12,211 record database resulting from this survey suggests that our list of 69 species is complete, with no evidence of rare species missed. For each species we provide:'¢A dichotomous key for identification.'¢Full-color figures.'¢Range maps at county scale.'¢Notes on habitat, ecology, life history, and reproductive biology.'¢Systematic and taxonomic updates to modern standards.

The distribution of commonness and rarity for this diverse and far-flung fauna did not appear lognormal, but rather bimodal, with a primary peak in the range of 16 ' 64 incidences and a secondary peak in the range of 256 ' 1,024. We propose a nonparametric system ranking our 69 species into five incidence categories, setting aside the rarest 5% and dividing the remainder into quartiles. Within this system we recognize subsets of peripheral (pseudo-rare) species and species demonstrating non-apparent rarity, following the work of K. J. Gaston. A new species of pleurocerid snail, Pleurocera shenandoa Dillon, is described in the appendix.