Two Genera of Carboniferous Echinoidea ( Lepidocidaris and Hyattechinus ) new to Britain

Abstract

Introduction The remains of echinoids occur at almost every horizon of crinoidal limestone in the Lower Carboniferous rocks of Britain; but they consist usually of isolated plates and radioles. Archæocidaris, Palœechinus, Perischodomus , and Lovenechinus must have thrived in our Carboniferous seas, and Melonechinus was by no means rare. But the conditions of deposition of the limestones, together with the collapsible nature of the tests, almost always resulted in disintegration and scattering of the remains. Only in the shaly facies of the Lower Carboniferous was the water sufficiently still, and sedimentation adequately rapid, to leave the component parts of echinoid tests in their natural association. Such conditions occurred in the Fifeshire area, where Mr. J. Wright has found fairly complete examples of the excessively fragile Lepidesthes together with great quantities of almost perfect crinoids. They also prevailed in the Bolland district of Lancashire, where Clitheroe has long been famed for its yield of crinoids, blastoids, and echinoids. A similar shaly development characterizes the “Lower Limestone Shales” and immediately succeeding strata at the base of the Carboniferous Limestone in South Wales. In this paper I am able to record an extraordinary find of echinoid tests at that horizon in Pembrokeshire. Perhaps the “Marbre noir de Dinant” may be cited as a neighbouring illustration of an argillaceous Carboniferous Limestone noteworthy for the wealth and preservation of its echinoid fauna. The abundance of echinoid fragments in the purer and more massive limestones shows that the sea-urchins lived quite as1 freely in the open water