PROC. ENTOMOL. SOC. WASH. 103(3). 2001. pp. 620-635 SEPEDON MCPHERSONl, N. SP., KEY TO NORTH AMERICAN SEPEDON, GROUPS IN SEPEDON S.S., AND INTRA-AND INTERGENERIC COMPARISON (DIPTERA: SCIOMYZIDAE) L. Knutson and R. E. Orth (LK) Systematic Entomology Laboratory, PSI, Agricultural Research Service, U.S. De-partment of Agriculture, Building 005, BARC-West, Beltsville, MD 20705, U.S.A.; cur-rent address: 4, Rue des Erables -34830 Clapiers, France (e-mail: [email protected]); (REO) Department of Entomology, University of California, Riverside, CA 92521, U.S.A.; current address: 26781 Kalmia Avenue, Moreno Valley, CA 92555, U.S.A. (e-mail: [email protected]) Abstract. — Sepedon mcphersoni, new species, from southern Illinois, U.S.A., is de-scribed and illustrated, and a key to the 20 North American species of Sepedon is pre-sented. The classification of the genus Sepedon and six related genera is discussed. All known species of Sepedon are classified in nine groups including the subgenus Parase-pedon Verbeke 1950 as the Trichrooscelis group, the subgenus Mesosepedon Verbeke 1950 as the Disperse: group, and the genus Sepedomyia Verbeke 1950 as the Nasuta group. A character matrix of the groups of Sepedon and related genera is included. Publications on the life cycles and/or immature stages of Sepedon and related genera are summarized. Key Words: snail-killing flies, taxonomy, classification, biocontrol agents The classification of snail-killing flies of the genus Sepedon Latreille in the Western Hemisphere was last revised by Steyskal (1951), who included 12 North American species and one subspecies. Since then, nine North American species have been de-scribed or their status has been changed (Steyskal 1960, 1965b; Fisher and Orth 1969, 1972, 1974; Orth 1986; Manguin 1990). Herein we describe a new species of Sepedon from Illinois, present a revised key to the species of North America, propose taxonomic groups for the species of Sepe-don worldwide, compare these groups with six related genera, and present a list of pub-lications on the life cycles and/or immature stages. The cosmopolitan genus Sepedon and re-lated genera are of special interest to evo-lutionary and behavioral studies of Scio-myzidae because certain species represent some of the most derived lineages within the family and because some are prime can-didates as biological control agents of dis-ease-carrying snails. Study of these genera is beginning to afford an opportunity to un-derstand the evolution of diverse modes of feeding behavior — from obligate parasit-oids to predators — by correlating feeding behavior with phylogenetic position estab-lished on the basis of morphological char-acter systems. As discussed below, indica-tions of the degree of relatedness and ge-neric and supra-generic characterizations have been provided in a few earlier studies of "Sepedon." A cladistic analysis of the family by Marinoni and Mathis (2000) con-firms or rejects some of those proposals and provides a more comprehensive basis for comparisons.