Abstract
Cyclostephanos numataensis sp. nov. i s described from the Numata paleo -lake deposit, inferred to be Upper Pleistocene in origin. The new species is characterized by an interfascicle, which has a rimoportula extending to the valve rim (sometimes a portion or all the interfascicles bearing fultoportulae have these structures positioned near the rim of each interfascicle). Internally, the rimoportula is positioned near the valve rim, and the external opening is on the mid mantle. External tubular extensions of the rimoportula and fultoportulae are lacking, and the ribs on the mantle interfascicles are plain.
