« Shell small, solid, oblong, tumid; anterior side rounded; posterior subtruncated; surface sculptured with from thirty-one to thirty-four finely granulated radial ribs, with interstices broader than the ribs; umbones slightly directed anteriorly; teeth numerous. » –Tokugana S.: “Fossils from the environs of Tôkyô”, Journal of the College of Science, Tokyo Imperial University vol. 21(2), Tokyo 1906, p.59.