Middle Ordovician bivalves from mid-Wales and the Welsh Borderland

The first middle Ordovician bivalve fauna to be described from Britain is f rom the lower part of the Didymograptus murchisoni Biozone of the Llanvirn Series of the Builth-Llandrindod Wells Inlier of mid-Wales. The fauna is pr eserved in a close inshore facies that accumulated locally around volcanic islands and is incorporated in bivalve-dominated shell-beds, some of which form true bivalve coquinas. The fauna is dominated numerically by palaeohet erodonts (including a single modiomorphoid species), but also includes seve ral species of palaeotaxodonts. Some forms of comparable age and some lower Ordovician species are described from the Shelve Inlier, Shropshire, and s ome basal upper Ordovician bivalves from mid-Wales are also described. The following new taxa are described: Praeleda subtilis sp. nov., Praeleda mult identata sp. nov., Arcodonta regularis gen. et sp. nov., Similodonta ceryx sp. nov., Eritropis peregrinata sp. nov., Glyptarca radnorensis sp. nov., C amnantia ampla gen. et sp. nov. and Modiolodon ellesae sp. nov.