A new genus and two new species of fresh water isopods from ground waters of the Kimberley region of West Australia are described. This new genus cannot be immediately assigned to an isopod suborder or family because its unique combination of characters encompass many plesiomorphies, as well as synapomorphies with the Flabellifera sensu lato. These features include free pleonites that are subequal except for an enlarged fifth pleonite, broad natatory pleopods, genital pores on medial extensions of the coxae, five pairs of oostegites, true coxal plates, an antennal protopod of three articles, and a rudimentary second flagellum on the antennula. One of the new species, well represented in one sample, is iteroparous and breeds continuously during the winter months. Because the type localities are from limestone fossil reefs not exposed to the marine environment since the Devonian period, these isopods may be remnants of an ancient freshwater stock. Name changes of some setal types are proposed.