The truly endemic North American earthworms, though they constitute only a small part of the total earthworm population, are almost all representatives of the family Megascolecidae. This family, a very ancient one, has spread widely throughout the tropics and the Southern Hemisphere and is there represented by a very rich fauna. North American members of the family, with the exception of a few peregrine species of tropical origin, belong to the genera Diplocardia, Plutellus, and Megascolides. Diplocardia' is considered a very primitive genus, constituting a group of indigenous species which occur throughout the Midwest and South as well as the Great Basin, Lower California and Mexico, where the genus presumably originated as early as the Jurassic and spread northward.2 Because of the fact that the few persons who have worked on North American earthworms have done most of their work in the Midwest, the Diplocandia are relatively better known than Plutellus and Megascolides. West of the Rockies, the native earthworm fauna falls in the genera Plutellus and Megascolides and is very much richer in forms than a review of the literature would indicate. The genotype of Plutellus, Plutellus h,eteroporus Perrier, was described in 1873 from two specimens collected in Pennsylvania more than 50 years earlier and oddly enough has never been recorded since, nor has any other species of this genus been collected in the eastern United States. In 1892, Benham described a species which he ascribed to the genus Plutellus from Queen Charlotte Is. Eisen (1894 and 1900) described Califomian species of a new genus, Argilophilus, which, though representing a distinct group of species (perhaps of subgeneric rank) has since been united with Plutellus. Michaelsen (1921) described a closely related species, also Californian. Megascolides was described from Australasia in 1878 and until 1897 all the species came from that region. Smith's description of M. americanus in that year was therefore of considerable interest. This genus, like Plutellus, presumably originated in Australia and spread by way of Siberia and Alaska to the Pacific Coast. Smith's (1897 and 1936) and Altman's (1937) papers on Oregon and Washington worms describe a number of species in these two genera, but the present authors' studies indicate that there is a wealth of undescribed material in this region. One species of Plutellus has been described from Guatemala3 and many species of Plutellus and Megascolides have been described from Australia, India and Tasmania.