Rostroconch molluscs are widespread and abundant in the Cambrian and Ordovician rocks of the Amadeus and Georgina Basins of northern Australia. Because the mollusc faunas of this area are largely unknown, this study concentrates on their systematics and biostratigraphic distribution. The work complements that of Pojeta, Runnegar (1976), who considered the known Cambrian and Ordovician rostroconchs from the rest of the world. We deal with 32 species, which are placed in 15 genera; 24 of the species are named and 8 are treated with open nomenclature. The 21 named species and 6 genera newly named here are: Ribeiria csiro sp. nov., R. hllckitta sp. nov., R. jonesi sp. nov., R. runnegari sp. nov., Apoptopegma dickinsi gen. novo et sp. nov., Cymatopegma semiplicatum gen. novo et sp. nov., Pinnocaris wellsi sp. nov., P. robllsta sp. nov., Ptychopegma burgeri gen. novo et sp. nov., Wanwania drllcei sp. nov., Technophorlls kempae sp. nov., T. nicolli sp. nov., T. planei sp. nov., T. walteri sp. nov., Kimopegma pinnatum gen. novo et sp. nov., Pallropegma gen. nov., Pleul'Opegma plicatum gen. novo et sp. nov., Tolmachovia beljordi sp. nov., Eopteria struszisp. nov., Euchasma caseyi sp. nov., E. skwarkoi sp. nov., and Bransonia chapronierei sp. Novo Twenty of the species are presently known only from the Georgina Basin, seven are known only from the Amadeus Basin, and five are common to both basins. The specimens were collected from 95 localities. The Australian occurrences are unusual in that 11 of the species are known from Upper Cambrian rocks; elsewhere in the world there are only four known species of rostroconchs in the whole Cambrian System. In the Cambrian rocks of Australia, four species of rostroconchs are known to occur in the Mindyallan Stage, one in the Idamean Stage, and seven in the Payntonian Stage. In the Australian Ordovician, ten species are known to occur in Datsonian rocks, four in Warendian rocks, and five in Arenigian rocks. Elsewhere in the world, most pre-Silurian rostroconchs occur in carbonate rocks; in Australia 14 of the known species occur in clastic rocks, and the remainder in carbonate rocks.
