Species [var. cynthia]: Cell body small, strongly curved, inner side concaved or straight at the centeral region, 73-180 μm long, 11-22 μm wide, L/W=8-10; cell wall brownish in color, finely striated (10-11 striae/10 μm); 3-5 pyrenoids in each semicell; [var. jenneri]: Cell body small, inner side concaved or straight at the centeral region, 43-(64-98)-110 μm long, 7-(8-11)-18 μm wide, cell wall smooth, transparent or brownish in color (Illustrations of The Japanese Fresh-water Algae, 1977). [var. curvatisssimum]: Strongly curved, central region nearly straight or slightly concave, tapered toward ends, both ends rounded, 88-137 μm long, 13-19 μm wide, L/W=6.5-9; cell wall lined (about 9 lines/10 μm); 5-6 pyrenoids in each semicell (Photomicrographs of the Freshwater Algae, vol.10, 1989).

31 μm 63 μm 94 μm; x 640

Images of collecting locality: Ohnuma (a pond in Ohnuma enchi), Nasu-shiobara city (formerly Shiobara town), Tochigi Pref., Japan, May 5, 2006, by Y. Tsukii