REVISION OF NORTH-AMERICAN AGABUS LEACH (COLEOPTERA, DYTISCIDAE) - THE OPACUS-GROUP

Species of the Agabus opacus- and lineellus-groups, as defined by Lars on (1989), are combined and revised as members of the A. opacus-group. The A. opacus-group contains 13 species, namely: A. hypomelas Mannerh eim, A. vancouverensis Leech, A. verisimilis Brown, A. vandykei Leech, A. wasastjernae (Sahlberg), A. opacus Aube, A. confertus LeConte, A. euryomus sp.nov., A. walsinghami (Crotch), A. jimzim sp.nov., A. linee llus LeConte, A. discors LeConte, and A. austrodiscors sp.nov. Agabus wasastjernae and A. opactus are Holarctic and boreal; the remaining 11 species are confined to the Cordilleran region of western North Ameri ca. Character distribution does not support recognition of subspecies of A. hypomelas, therefore A. hypomelas irregularis Mannerheim is rega rded as a synonym of A. hypomelas. A lectotype is designated for A. di scors LeConte. A phylogenetic tree of the hypothesized relationships b etween the species is presented. A key to the species of the group is included. For each species, the following information is provided: syn onymy; description and illustration of taxonomically important charact ers; notes on relationships, variation, distribution, and ecology; and a map of North American collection localities.