Genus: Cell body small, length = width, strong constriction at its center; semicells inverted triangular, ellipsoidal, rectangular, etc. in shape; straight or slightly curved spiny projections at each corner; one pyrenoid in each semicell; cell wall smooth (Illustrations of The Japanese Fresh-water Algae, 1977). Species: Semicells inverted semicircle or hexagon in shape; (Illustrations of The Japanese Fresh-water Algae, 1977).

31 μm 63 μm 94 μm; x 640

Images of collecting locality: Utsubo-numa (a pond), Zao mountain, Zao onsen, Yamagata city, Yamagata Pref., Japan, July 13, 2008 by Y. Tsukii