Abstract
A new fossil diatom species Cyclotella kitabayashii H.Tanaka sp. nov. is described from Pliocene sediment of the Tsubusagawa Formation in Kyushu, southwestern Japan. The new species is characterized by larger circular valves and smaller elliptical valves, valve faces that are tangentially undulate with fultoportulae arranged in a circular pattern in the central area with many areolae. Internally, there are alveolae in the marginal area. Every costa or every second (rarely third) costa is recessed and bears a fultoportula. Valve face and mantle fultoportulae have uniquely shaped satellite pore covers. The authors were unable to find any taxon that has the combination of these characteristics and accordingly propose C. kitabayashii as a new species. The new species is compared to similar taxa.
