A new genus, Graliophilus, is erected for the Western Australian section of Plutellus and five species-groups are defined within the new genus, at least two of which may merit elevation to generic rank. Two new species, G. georgei and G. secundus are referred to a southerly species-group of Graliophilus while new material of Plutellus strelitzi Michaelsen is assigned to a second, more northerly species-group. Redescription of type-material of P. candidus Jackson and of P. varicystis Jackson reveals that the former belongs to the strelitzi group and the latter to the georgei group. New material of Woodwardiella molaeleonis (Michaelsen) is described and permits elucidation of the morphology of the excretory system of the genus. A very distinct new species W. acanthodriloides is described from the Frankland River far to the south of the Swan basin range of the callichaeta group to which W. molaeleonis belongs. The new genus Austrohoplochaetella is erected for a new species from Cape Range. This genus is allied to Megascolides but possesses longitudinal proctodaeal excretory ducts. The genus Pseudonotoscolex is erected for a new species, from the Pallinup River, which lacks the alimentary characteristics of Notoscolex. The zoogeography of the 11 megascolecid genera known from Western Australia is briefly discussed. The seven genera with endemic species have limited and distinctive distributions within the south-western province and this is shown to be true of the five species-groups of Graliophilus. Three genera, and possibly also Woodwardiella Stephenson, are endemic and it is expected that a higher endemicity will be demonstrated on revision of several genera. Ignoring the anthropochorous Pheretima, all but four, circurnmundane, species of the 53 megascolecid species recorded from Western Australia are restricted to the subregion.