<i>Yunfuconcha</i> new genus, a possible stem-archiheterodont bivalve from the Ordovician of Guangdong, South China

ABSTRACT Yunfuconcha bimenta, a new genus and species of bivalve from the Ordovician of western Guangdong, China, is described. Its unusual hinge consists of a palaeotaxodont-like dentition anteriorly and a heteroconch-like dentition posteriorly. The posterior hinge area exhibits a remarkable, broad, deeply inset, concave ligament area, which is reminiscent of the ventrally expanded ligament of some Recent and fossil lucinoids and the triangular resilifer in late Palaeozoic crassatellid heteroconchs. Lamellar posterior teeth and sockets complete the posterior dentition. The unusual combination of features, normally associated with either the Order Cardiolariatida (used here in place of Order ‘Afghanodesmatida’—the type genus Afghanodesma, is known only from wax impressions rendering it and its nominal higher taxa invalid) or various crassatelloids and lucinoids, make systematic placement of Yunfuconcha n. gen. uncertain below subclass rank. In view of presumed derived heteroconch-like characters of the posterior hinge, we place Yunfuconcha n. gen. in the Subclass Autobranchia, possibly as a stem archiheterodont or a stem heteroconch.