Tertiariopsis nipponicus sp. nov., from a pliocene freshwater deposit in southwestern Japan

Tertiariopsis nipponicus sp. nov. is described from a Pliocene deposit of the Tsubusagawa Formation, southwestern Japan. The species is characterized by its convex or concave central part of valve face often slightly offset from the geometric valve center, one valve face fultoportula, areolae arranged in radial rows forming fascicles at the valve margin and areolae on valve face larger than those of mantle. Internally, one valve face fultoportula with two satellite pores situated near valve center, areolae having occluded domed cribra, interfascicles slightly raised at valve margin with every second or third one extending to the lamina-covered valve edge where a mantle fultoportula with three satellite pores is located. A single rimoportula is located at the end of an interfascicle on the mantle. All processes lack outer tubes. The cinglum consists of four bands. This new taxon is compared to three similar species of Tertiariopsis.