Subgenus: Atomum (Apical area slightly depressed) Section: Simplicia (Cell body small; cell surface smooth) Species: Cell body small, 15-30 μm long, 12.5-21 μm wide, constriction 3-8 μm wide, L/W=1.3; semicells pyramidal in shape, basal lobes rounded, anterior margin broad, slightly depressed at the center, both corners slightly pointed; lateral view of the semicells ovoidal, apical view ellipsoidal, both sides convex (Illustrations of The Japanese Fresh-water Algae, 1977).

31 μm 63 μm 94 μm; x 640

Images of collecting locality: waterfield between Kita-Omachi station and Nogu river, Omachi city, Nagano Pref., Japan, June 4, 2007 by Y. Tsukii