A single incomplete skull, fragments of two skull roofs, parts of the opercular series, two complete mandibles, and several fragmentary mandibles covering a considerable size range, form the basis of this description of Speonesydrion (type species S. iani Campbell and Barwick). They come from the base of the Receptaculites Limestone or the top of the Bloomfield Limestone in the Taemas Group at Wee Jasper, New South Wales. The skull roof has characters intermediate between the dipnorhynchid and dipterid grades. The teeth, best known from the mandibles, are in radial rows of variable definition, and are firmly attached to the underlying bone without any sign of a basal pulp cavity. The mode of growth of the tooth plates can be followed through a series of growth stages, and this sheds light on the course of evolution of early dipnoan dentitions.
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