This is the first American Fisheries Society conservation assessment of freshwater gastropods (snails) from Canada and the United States by the Gastropod Subcommittee (Endangered Species Committee). This review covers 703 species representing 16 families and 93 genera, of which 67 species are considered extinct, or possibly extinct, 278 are endangered, 102 are threatened, 73 are vulnerable, 157 are currently stable, and 26 species have uncertain taxonomic status. Of the entire fauna, 74% of gastropods are imperiled (vulnerable, threatened, endangered) or extinct, which exceeds imperilment levels in fishes (39%) and crayfishes (48%) but is similar to that of mussels (72%). Comparison of modern to background extinction rates reveals that gastropods have the highest modern extinction rate yet observed, 9,539 times greater than background rates. Gastropods are highly susceptible to habitat loss and degradation, particularly narrow endemics restricted to a single spring or short stream reaches. Compilation of this review was hampered by a paucity of current distributional information and taxonomic uncertainties. Although research on several fronts including basic biology, physiology, conservation strategies, life history, and ecology are needed, systematics and curation of museum collections and databases coupled with comprehensive status surveys (geographic limits, threat identification) are priorities.

A complete, annotated listing of all primary and secondary type specimens of gastropod mollusks (exclusive of opisthobranchs and pulmonates) in the collection of the Division of Invertebrate Zoology at the American Museum of Natural History (AMNH) (as of December 31, 1999) is presented. Supplementary listings for bivalves and opisthobranch gastropods (previously covered in Part 1) are also given. This catalog includes 1309 type lots, 18 lectotype designations, and illustrations for 12 previously inadequately illustrated type specimens and five species never before illustrated. New synonymy information is given for nine species, one species is shown to be a valid name, one new replacement name is introduced, and one neotype is suppressed with rediscovery of type material. An appendix of AMNH specimens previously incorrectly cited as types is also given. An index of genera and species is included for each class and subclass.

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The diversity of freshwater mussels in Colorado is low compared to other regions of the U.S.A., with only three extant species (down from seven a century ago). The western ridged mussel (Gonidea angulata) occurs in Pacific Coast drainages from British Columbia to California and eastward to Idaho and Nevada. It has been reported from Colorado based on a single museum specimen from Clear Lake, representing a significant range expansion for this species. During extensive recent surveys, 1 was unable to pinpoint this locality and regarded it as questionable. Examination of the specimen and locality data indicated this specimen was collected from Clear Lake, Lake County, California.