Abstract:An organic-walled microphytoplankton species, Comasphaeridium Magnum sp. nov., recently discovered in petrographic thin scctions of the Doushantuo Formation (Late Sinian, about 700 Ma old) of western Hubei Province, South China are described here. This discovery supplements our understanding of the Doushantuo microblota, and shows that the Doushantuo Formation is the lowest stratigraphic position of the genus Comasphaeridium Staplin, Jansonius and Pocock so far known in the world.