Cosmarium formosulum Hoffmann var. formosulum: Cell body (34)-40-50 μm long, (34)-40 μm wide, isthmus 10-(11)15.5 μm wide, (Illustrations of The Japanese Fresh-water Algae, 1977).
Cosmarium formosulum var. mesochondrium (Schmidle) Hirano: Cell body 37.8-39 μm long, 30-31 μm wide, isthmus 9.8-11 μm wide, (Illustrations of The Japanese Fresh-water Algae, 1977).