Synopsis of the riffle beetle genus Zaitzevia (Coleoptera : Elmidae) in North America, with description of a new subgenus and species

Zaitzevia is represented in the Western Hemisphere by a rather variable spe cies, Z. parvula which ranges from the Yukon of Canada southward to norther nmost Mexico and from the Pacific coast eastward to the Black Hills of Sout h Dakota and the Niobrara River of Nebraska. A new species from the Pacific Northwest, Z posthonia, is sufficiently different from all other known spe cies of Zaitzevia to merit erection of a new subgenus, Suzevia. The most di stinctive feature of Suzevia is the form of the penis, which is basally swo llen rather than slender and cylindrical.