Species [Ralfs f. quadratum]: Cell body 48-(53-73) μm long, 25-(28-40) μm, isthmus 12-(20-26) μm wide, L/W=2; bay opening closed; semicells rectangular, rounded at base with frontal slight depression; apical corners broadly rounded; side view elliptical or oval; apical view elliptical; cellwall smooth. [f. willei W. et G.S. West] Cell body 50-(55-82) μm long, (30-36.5)-40 μm, isthmus 17-27 μm wide, bay slightly opened; side margins of semicells nearly straight lacking slight depression at base (Illustrations of The Japanese Fresh-water Algae, 1977).

31 μm 63 μm 94 μm; x 640

Images of collecting locality: Tane-ike (pond), Togakushi highland, Shinano town, Nagano Pref., Japan, May 21, 2006 by Y. Tsukii