Species [ var. formosulum ]: Cell body small, trapezoid in shape, basal margins broadly rounded, both sides crenated with 6-7 projections, apex slightly wavy (5 waves), (34)-40-50 μm long, (34)-40 μm wide, isthmus 10-(11)15.5 μm wide; cell wall granulated; semicells with about 5 longitudinal ridges at the center, granules present on each ridge, side view ovoid (Illustrations of The Japanese Fresh-water Algae, 1977). [var. mesochondrium]: 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).

31 μm 63 μm 94 μm; x 640

Images of collecting locality: Rice field near Lake Nakatsuna, Omachi city, Nagano Pref., Japan, June 1, 2008 by Y. Tsukii