Diceratidae Dall 1895

FamilyDiceratidae Dall, 1895 Remarks. The Diceratidae are the stem group of all uncoiled rudists (Skelton 2013 a). The characteristic combination of right-valve attachment, sub-equivalve to inequivalve shells, external parivincular ligament and outward-coiled prosogyrate umbos is restricted to the genera Diceras Lamarck, 1805 and Valletia Munier-Chalmas, 1873 (Skelton and Smith 2000; Skelton 2013 b; Schneider and Skupien 2015).