Morphology and taxonomy of the late Silurian rhynchonellide brachiopod Notoconchidium

The distinctive brachiopod genus Notoconchidium is known from late Silurian, mostly sandy, shallow marine strata in Tasmania, Victoria and New Zealand. Material from the Zeehan and Wynyard areas (Tasmania), the Whittlesea-Wallan and Heathcote areas (Victoria), and the Wangapeka River area (New Zealand), permits further insight into detailed aspects of morphology and relationships between the previously named species N. tasmaniense, N. florencense and N. thomasi. We conclude that N. thomasi is a junior synonym of N. tasmaniense, but N. florencense is retained as a separate species. New species described are N. talenti and N. argentium. The diamond-shaped septalium of Notoconchidium exhibits, depending on the degree of calcification, either an anteriorly located perforation interpreted as the surface end of a tube extending to the dorsal umbo, or a deep, anteriorly located notch, both presumably housing dorsal adjustor muscles. Bifurcation of costellae is irregularly developed and is considered taxonomically insignificant. Possible brood pouches are noted in some dorsal valves.