Bryelmis Barr, a new genus of elmid, and three new species, Bryelmis idahoensis Barr, Bryelmis rivularis Barr, and Bryelmis siskiyou Barr, are described from streams and springs in Washington, Oregon, California, and Idaho. Drawings or photographs of the adult habitus and male genitalia of each species, and of the larval habitus of the genus, are included, as well as a key to the adults of the species and revised couplets for insertion into existing adult and larval keys to the Elmidae. The biogeography, habitat, and microhabitat of the species are discussed. Aquatic liverworts are the unusual primary microhabitat of all three species of Bryelmis.