Abstract
A Devonian horizon near Reefton yields numerous Nuculoidea vespa n.sp. and Nuculoidea umbra n.sp. The large size range of these fossils allows pericardial and pedal muscle scars to be distinguished during ontogeny. In larger specimens, the pericardial muscles become buttressed by a strong trans-umbonal plate. Both species of Nuculoidea are inequivalve. This character is seen particularly in the placement of the anterior retractor muscle scars of Nuculoidea vespa, and is thought to be related to a life position in which the animal lay on one valve.

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