Abstract
A recently found Stephanodiscus fossil, S. uemurae sp. nov., from Mio-Pliocene sediment of the Miyata Formation, Senboku City, Akita Prefecture, northern Honshu, Japan is described here. The new species is characterized by having a slightly double concentric undulation of the valve face, uniseriate fascicles at the valve center and biseriate or triseriate fascicles at the valve face/mantle junction. There is often a slight break between the rows of areolae on the valve face and mantle. Usually, there are no valve face fultoportulae. Spines are located on all interfascicles at valve face/mantle junction except in the case where openings of mantle fultoportulae are present, which is usually every two or three interfascicles. One tubular rimoportula replaces a spine and is located slightly above the ring of spines. The new species is illustrated with LM and SEM photographs.
