Pelecypod molluscs are widespread and reasonably abundant in the Ordovician rocks of Tasmania and the Amadeus and Georgina Basins of northern Australia. Because the mollusc faunas of these areas are not well known, this study concentrates on their systematics. We deal with 47 species of pelecypods, which are placed in 31 genera; 38 species are named and nine are treated within open nomenclature. Twenty-seven of the named species and 20 of the genera are newly named herein: Ctenodonta youngi sp. nov., C. macalesteri sp. nov., Alococoncha gen. nov., Fidera maryae gen. novo et sp. nov., Deceptrix banksi sp. nov., Eritropis gen. nov., Inaequidens davisi gen. novo et sp. nov., I. campbelli sp. nov., lohnmartinia cordata gen. novo et sp. nov., Lophoconcha gen. nov., Palaeoneilo smithi sp. nov., Sthenodonta jelli gen. novo et sp. nov., S. passmoreae sp. nov., Zeehania jacksoni gen. novo et sp. nov., Cyrtodonta carberryi sp. nov., C. hazeli sp. nov., C. stafJordae sp. nov., Cyrtodontula hadzeli sp. nov., C. sohli sp. nov., Pharcidoconcha raupi gen. novo et sp. nov., Leconychia doylei gen. novo et sp. nov., Glyptonychia wilsoni gen. novo et sp. nov., Pteronychia haupti gen. novo et sp. nov., Denticelox gen. nov., Runnegaria cuneata gen. novo et sp. nov., Colpantyx woolleyi gen. novo et sp. nov., Xestoconcha kraciukae gen. novo et sp. nov., Copidens browni gen. novo et sp. nov., Brachilyrodesma radkei gen. novo et sp. nov., Noradonta shergoldi gen. novo et sp. nov., and Sphenosolen draperi gen. novo et sp. novo The eleven species named by Tate (1896) and Iohnston (1888) are considered, and their generic-level assignments are updated. The species 'Pteronites' micans Tate is based on the genal spine of a trilobite and is not a pinnid pelecypod. A new family Colpomyidae is erected within the superfamily Mytilacea. Twenty-six of the species are at present known only from the Amadeus Basin, nine only from the Georgina Basin, and two (possibly three) are common to both basins. Ten species are known from Tasmania, none of which are in common with mainland Australian spocies. The specimens were collected from 91 localities. The age of the pelecypods ranges from Early Ordovician (Arenigian) to Late Ordovician (Richmondian); most species occur in lower Middle Ordovician rocks. Most of the Tasmanian species are found in limestones, whereas most of those from the mainland are in coarse clastic rocks. In addition to the pelecypods, we comment briefly on six species of rostroconch molluscs, two of which are newly named: Tolmachovia corbetti sp. novo and Bransonia townleyi sp. Novo.
