Article: New Silurian neotaxodont bivalves from South Wales and their phylogenetic significance
V. Alexander Ratter and John C. W. Cope
The arcoidean bivalves, Trecanolia acincta gen. et sp. nov. and Uskardita mikraulax gen. et sp. nov., are described from the Wenlock of South Wales. These bivalves are accommodated within the new family Frejidae, alongside the closely related Silurian genera Freja Liljedahl and Alytodonta Cope. The frejids are characterized by an amphidetic, chevron-shaped duplivincular ligament, and a ventrally diverging dental arrangement of pseudocardinals and pseudolaterals. The group provides further evidence that the superfamily Arcoidea evolved from an early Ordovician ancestor, such as Catamarcaia Sanchez and Babin. The frejids represent an early diversification of the arcoideans, previously unknown in the Palaeozoic.