A great deal of confusion exists over the status of many of our eastern Australian Permo-Carboniferous genera of Pelecypoda. This chaotic state is particularly pronounced in the genera described by J. D. Dana in 1847, mainly Cleobis, Cypricardia, Pyramus, and Myonia, as well as other closely allied genera. Many of these forms were described from small series of not exceptionally well preserved specimens, and it is only to be expected that errors in synonymy, in a doubtful genus, will occur as time proceeds.
The Australian Museum collection of Permo-Carboniferous Pelecypoda has lately been augmented by the purchase of several large palaeontological collections, consisting for the most part of the Varney Parkes and the John Mitchell collections, and these have considerably enhanced the working value of the collection on which this paper is based. This series, together with material and advice from Mr. W. S. Dun, Government Palaeontologist of New South Wales and Lecturer in Palaeontology at the University of Sydney, has enabled me to attempt to unravel these dubious genera. The plaster casts or replicas of Dana's type specimens obtained by the Australian Museum from the United States National Museum, Washington, have also been of material assistance in the compilation of this work.