Upper Miocene Echinoids from the Yorktown Formation of Virginia and Their Environmental Significance

Abstract

Five echinoid species are described from the upper Miocene part of the Yorktown Formation of Virginia: <i>Echinocardium orthonotum</i> (Conrad), <i>Arbacia imporcera</i> (Conrad), <i>Psammechinus philanthropus</i> (Conrad), <i>Mellita aclinensis</i> Kier, and <i>Spatangus glenni</i> Cooke. The assemblage probably lived in shallow, warm-temperate waters, <i>E. orthonotum</i> deeply buried near shore, <i>S. glenni</i> shallowly buried offshore, and <i>M. aclinensis</i> with its test just covered near shore. <i>Arbacia improcera</i> and <i>P. philanthropus</i> presumably lived together intertidally and near shore, <i>P. philanthropus</i> living in holes in the indurated sediments or on the sand with its test covered with debris, whereas <i>A. improcera</i> probably was easily visible with nothing covering its test. Specimens formerly referred to <i>E. orthonotum</i> from the middle Miocene Choptank Formation from Maryland are referred to <i>E. marylandiense</i>, new species. <i>Echinocardium gothicum</i> (Ravenel), from the Bear Bluff Formation of South Carolina, is considered a junior subjective synonym of <i>E. orthonotum</i>.