The Permian bivalve genera Myonia, Megadesmus, Vacunella and their allies, and their occurrences in New Zealand (print copy)

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Waterhouse, J.B. 1969 The Permian bivalve genera Myonia, Megadesmus, Vacunella and their allies, and their occurrences in New Zealand. Wellington: New Zealand Geological Survey. New Zealand Geological Survey paleontological bulletin 41 141 p.

Abstract: The Permian bivalve genera Megadesmus, Myonia, Vacunella and their allies are described and compared on the basis of examination of all available type material. They are considered to be most closely related to Edmondia. One group of genera (Myonia Dana, Pachymyonia Dun and allies) are shown to have edentulous hinges, and are referred to the Edmondiinae. The affinities of the genus Vacunella Waterhouse 1965 lie probably with Chaenomya Meek, referred to subfamily Chaenomyinae and placed tentatively in the Edmondiidae on the apparent presence of an internal ligament groove. A third group of genera with an inner ligament, Megadesmus Sowerby, Pyramus Dana, Notomya M’Coy, and Globicarina Waterhouse (if this is not synonymous with Megadesmus) share a rudimentary tooth in the right valve, and are assigned to the Pachydominae of Fischer, 1887. They presumably developed from Edmondia stock in the Carboniferous. Astartila Dana and Pleurikodonta Runnegar are referred with Scaldia de Ryckholdt to a new subfamily Astartilinae, distinguished by musculature and the presence of one or more teeth in each valve. Morphological details for each genus are described from the type species, supplemented by details from allied species. A neotype is proposed and new description given of the Australian species Edmondia nobilissima de Koninck, and a new Australian species is described as Globicarina sp. nov. Notomya ovalis M’Coy is illustrated for the first time, and Notomya trigonalis Johnston redescribed. The evolution within each genus is traced, particularly for species from India, Australia, and New Zealand. A new subgenus Myomedia is erected for Pachydomus carinatus Morris 1845 and a new genus Myofossa for Myonia subarbitrata Dickins 1963 (probably Sanguinolitid). From New Zealand four species and fragments are recorded from the basal Wordian Letham Formation, three from the Wordian Flowers Formation, and 17 species and two subspecies from the Wordian Mangarewa Formation. Additional fragments are listed from the Mangarewa Formation and from the Capitanian Arthurton and Bryneira Groups. Newly described taxa from New Zealand are Myonia compacta, M. ovata, Pachymyonia triangulata, Vacunella curvata ornata, V. oblonga, and Notomya gigantissima. Eight of the remaining species in New Zealand are referred to species named from eastern Australia, chiefly New South Wales, and most of the remainder are too incompletely preserved to be identified. (auth)

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