A new genus of discoidal diatom with rimoportulae arranged in opposite arcs (Coscinodi s cales)

Abstract

Arcusidiscus oppositus gen. et sp. nov. is described from the early Miocene sediments of the Boso Peninsula, central Japan. In addition to those in a marginal ring, there are three to six rimoportulae aligned in short arcs. Their location away from the valvar margin distinguishes this new genus from those with saucer-shaped valves.