A giant new trimerellide brachiopod from the Wenlock (Early Silurian) of New South Wales, Australia

Keteiodoros bellense n.gen. and n.sp. is a remarkably large trimerellide brachiopod from the Wenlock Dripstone Formation, southeast of Wellington, central New South Wales. The probable articulatory mechanism is unusual for trimerellides. It apparently involved both flattened sections of the lateral commissures which acted as pivots for opening and closing the shell, and a large and strongly modified articulating plate (which partly envelopes a robust dorsal umbo) articulating with the pseudointerarea at the posterior end of the ventral platform. The heavy dorsal umbo probably acted as a counterbalance to the anterior part of the valve; the diductor muscles were apparently attached to the umbo at the sides of the articulating plate, and to the anterior end of the ventral platform. The trimerellides occur in presumed life position in nearly mono specific beds which are interpreted as having formed in a quiet inshore shallow subtidal area on a sloping shelf, protected by coral biostromes but periodically disrupted by storm action. They are considered to represent a low-diversity quietwater Benthic Assemblage 2 community.