Abstract
A new fossil diatom species, Tetracyclus radius sp. nov, is described from freshwater sediments under the Yamato Bank in the Japan Sea. Its valve outline is circular with radiating costae and has a single rimoportula. There is no distinct sternum but a hyaline central area is present. The freshwater sediments are deposited before the Early Pliocene by diatom biostratigraphy of the overlying marine sediments.
