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We analysed cytochrome c oxidase subunit I and NADH dehydrogenase subunit I sequence variation among 29 populations of a widely ranging southwestern springsnail (Pyrgulopsis micrococcus) and 18 regional congeners. Cladistic analyses of these sequences depict P. micrococcus as a polyphyletic composite of five well-supported clades. Sequence divergences among these clades and subclades imply the possible occurrence of as many as seven or eight cryptic species in addition to P. micrococcus. Our finding that P. micrococcus contains multiple, genetically distinct and geographically restricted lineages suggests that diversification within this highly speciose aquatic genus has been structured in large part by the operation of terrestrial barriers to gene flow. However, these sequence data also indicate that recent dispersal among hydrographically separated areas has occurred within one of these lineages, which we attribute to passive transport on migratory waterbirds.

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SERIES PUBLICATIONS OF THE SMITHSONIAN INSTITUTION Emphasis upon publication as a means of "diffusing knowledge" was expressed by the first Secretary of the Smithsonian. In his formal plan for the institution, Joseph Henry outlined a program that included the following statement: "It is proposed to publish a series of reports, giving an account of the new discoveries in science, and of the changes made from year to year in all branches of knowledge." This theme of basic research has been adhered to through the years by thousands of titles issued in series publications under the Smithsonian imprint, commencing with Smithsonian Contributions to Knowledge in 1848 and continuing with the following active series: Smithsonian Contributions to Anthropology Smithsonian Contributions to Botany Smithsonian Contributions to the Earth Sciences Smithsonian Contributions to the Marine Sciences Smithsonian Contributions to Paleobiology Smithsonian Contributions to Zoology Smithsonian FoUdife Studies Smithsonian Studies in Air and Space Smithsonian Studies in History and Technology In these series, the Institution publishes small papers and full-scale monographs that report the research and collections of its various museums and bureaux or of professional colleagues in the world o^ science and scholarship. The publications are distributed by mailing lists to libraries, universities, and similar institutions throughout the world. Papers or monographs submitted for series publication are received by the Smithsonian Institution Press, subject to its own review for format and style, only through departments of the various Smithsonian museums or bureaux, where the manuscripts are given substantive review. Press requirements for manuscript and art preparation are outlined on the inside back cover.

Hershler, Robert, and Winston F. Ponder. A Review of Morphological Characters of Hydrobioid Snails. Smithsonian Contributions to Zoology, number 600, 55 pages, 21 figures, 1998.-We provide herein a description of morphological characters of aquatic gastropods of the family Hydrobiidae and of several other families of Rissooidea that resemble these snails in general features. The hydrobiid gastropods comprise the largest group of freshwater mollusks, with more than 1,000 species and more than 400 Recent and fossil genera. This compilation is a prelude to the first rigorous phylogenetic analysis of the higher taxa of this cosmopolitan, yet poorly understood, group, for which at least 70 family-group taxa have been proposed. It also was prepared to fulfill a need for standardization of terminology and interpretation of characters used in taxonomic descriptions of these small, often morphologically simple, snails. Given that taxonomic study of these animals has long been hampered by reliance on a limited number of morphological features, all aspects of the shell and the soft-part anatomy are reviewed as part of this treatment, and we attempt to be maximally inclusive in listing characters. Emphasis is placed on characters considered potentially useful in recognizing and defining hydrobiid clades, although features having utility for species-rank descriptions are summarized in an appendix. For 202 characters, sufficient information was available to delineate states and tentatively identify plesiomorpbic conditions (based on outgroup comparisons). Features utilized are from the shell (29 characters), operculum (13), external features (32), pallial cavity (10), digestive system (29), life history (6), female reproductive system (52), and male reproductive system (31). Discussion of many characters is augmented by schematic diagrams and in almost all cases by reference to taxa and published figures illustrating given states. Many characters are extensively annotated, and in some cases new concepts of homology and/or division of characters are proposed. OFFICIAL PUBLICATION DATE is handstamped in a limited number of initial copies and is recorded in the Institution's annual report, Annals of the Smithsonian Institution. SERIES COVER DESIGN: The coral Montastrea cavernosa (Linnaeus).