Middle Ordovician bivalves from mid-Wales and the Welsh borderland

Abstract

The first middle Ordovician bivalve fauna to be described from Britain is from the lower part of the Didymograptus murchisoni Biozone of the Llanvirn Series of the Builth-Llandrindod Wells Inlier of mid-Wales. The fauna is preserved 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 palaeoheterodonts (including a single modiomorphoid species), but also includes several species of palaeotaxodonts. Some forms of comparable age and some lower Ordovician species are described from the Shelve Inlier, Shropshire, and some basal upper Ordovician bivalves from mid-Wales are also described. The following new taxa are described: Praeleda subtilis sp. nov., Praeleda multidentata sp. nov., Arcodonta regularis gen. et sp. nov., Similodonta ceryx sp. nov., Eritropis peregrinata sp. nov., Glyptarca radnorensis sp. nov., Camnantia ampla gen. et sp. nov. and Modiolodon ellesae sp. nov.