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In this volume the authors report the results of the largest-scale inventory of freshwater snails ever conducted in the United States. They have reviewed and synthesized macrobenthic collections taken by ten natural resource agencies, malacological holdings at eight museums, and their 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 the list of 69 species is complete, with no evidence of rare species missed. For each species the authors provide:
- A dichotomous key for identification.
- Full-colour 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. The authors 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 they 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.
Dr. Robert T. Dillon, Jr. is America's foremost authority on freshwater gastropods. From 1983 until retirement in 2016 he was professor of biology at the College of Charleston in South Carolina. He is the author of The Ecology of Freshwater Molluscs (Cambridge University Press, 2000) and over 60 scientific papers on the genetics, evolution, and ecology of snails. A former president of the American Malacological Society, Dr. Dillon contributed the freshwater gastropod chapter to the popular 2006 AMS publication, The Mollusks: A Guide to their Study, Collection and Preservation. In 1998 he founded the Freshwater Gastropods of North America Project, a long-term, collaborative effort to inventory and monograph the entire gastropod fauna inhabiting every river, lake and stream throughout the continent north of Mexico.
