A new polydesmid milliped genus and two new species from Oregon and Washington, U. S. A., with a review of Bidentogon Buckett and Gardner, 1968, and a summary of the family in Western North America (Polydesmida: Polydesmidae)

In North America west of the Continental Divide, the milliped family Polydesmidae consists of six genera and 15 species, and occupies eight disjunct areas. Retrorsia, n. gen., is proposed for two new “micro-polydesmid” species (R. leonardi, the type species, and R. benedictae) in western Oregon and Washington, primarily in the lower Columbia River Valley. It is most closely related to Utadesmus Chamberlin and Hoffman, 1950, in Utah and New Mexico, and is characterized primarily by a retrorse gonopodal tibiotarsus that curves dorsad and counters the ventral curvature of the telopodal stem. New records are presented for the coastal species of Bidentogon Buckett and Gardner, 1968, occurring from Mendocino to Santa Cruz counties, California, and encompassing the area around San Francisco Bay. The oldest available name for this species is californicus (Chamberlin, 1918), whose type locality is Stanford, Santa Clara County. This name has been misapplied to the species occurring in Sacramento County, herein named B. expansus, n. sp., and B. helferorum Buckett and Gardner, 1968, is placed in synonymy under B. californicus.