New range information on two West American slugs (Gastropoda: Pulmonata: Arionidae) by Barry Roth and Peter H. Pressley. Bull. Southern California Acad. Sci. 82(2):71-78, 1983. Prophysaon dubium Cockerelh 1890. occurs in rockslides in the vicinity of Big Bar. Trinity County. California. This is the first record of the species in California and a range extension south approximately 375 km from near Cheshire, Lane County, Oregon. Hesperarion niger (Cooper 1872) occurs at the same locality, a range extension north-northwest about 195 km from Williams. Colusa County. California. Seven localities in southern Monterey and northern San Luis Obispo counties. California, document the southern range of H. niger in the Coast Ranges; three new localities in the Sierra Nevada are added. The known distribution of H. niger is mapped.