Because of similarities in their accessory musculature, dentition, ligament structure, micro-ornament, and shape, the Australian Permian bivalves Megadesmus Sowerby and Astartila, Pyramus, and Myonia Dana appear to have been shallow-burrowing relatives of the deep-burrowing bivalve Vacunella Waterhouse, so that they can now be included in the same family. In view of previously recognised similarities between Vacunella and the Mesozoic and Cainozoic genus Pholadomya, it is considered herein that the late Palaeozoic edmondioid bivalves gave rise to the Mesozoic and Cainozoic pholadomyoids, and that these two groups together constitute a major division of the Class Bivalvia - a division that may have been relatively distinct since Ordovician time.
Pachydomus Morris, Cleobis Dana, and Globicarina Waterhouse are considered to be major synonyms of Megadesmus, although Cleobis is tentatively retained as a subgenus of Megadesmus. Notomya McCoy, Pyramia Dana, and Clarkia de Koninck are synonyms of Pyramus, and Maeonia Dana and Pachymyonia Dun are synonyms of Myonia. A new genus, Pleurikodonta (type species P. elegans sp. nov.), is proposed for small radially ornamented shells internally similar to Astartila, and Vacunella is used for species previously referred to Chaenomya Meek. Myonia carinella, Myonia? sulcata, and Vacunella? dawsonensis are new species from eastern Australia.
A revisionary study of the Permian Pectinacea of eastern Australia has resulted in the erection of two new species of Aviculopecten (A. fletcheri and A. dawsonensis) and one new species of Streblochondria? (S? microsculptilis). Genera not previously recorded from eastern Australia are Cassianella Beyrich (C, queenslandica sp. nov.) and Cyrtorostra Branson (C, bowenensis sp. nov.), and the Western Australian Permian species Deltopecten waterfordi and Eurydesma playfordi are now known from Tasmania and Queensland respectively.
Glendella (type species G. dickinsi sp. nov.) is proposed for a strongly inequivalved shell that appears to have been derived from Eurydesma in the upper Artinskian. It is considered to represent a second member of the Family Eurydesmidae and supports the proposed transfer of the Eurydesmidae from the Mytilacea to the Pectinacea.
Five distinct marine faunas are recognised in the Permian of eastern Australia. The oldest, the Allandale fauna, is restricted to the Sydney Basin and Tasmania but occurs at Durras South on the South Coast of New South Wales, suggesting that the base of the sequence in that area is older than has previously been thought. It is succeeded by Faunas II and IV of Dickins in the Sydney Basin and Tasmania, and by Faunas II, III, and IV in the Bowen Basin. The interval corresponding to Fauna III in the Sydney Basin contains a mixture of species restricted to Faunas II and IV in Queensland and is characterised by the concurrent ranges of Eurydesma and Myonia corrugata. Recent discoveries of species of Uraloceras and Neocrimites in Queensland have assisted in the correlation of these faunas with the type Permian sequences in the Ural Mountains, Russia.