Species: 250-(396-576)-790 μm long, 25-(33-84) μm wide; cell body large, slightly curved; both termini tapered; pyrenoids 7-15 in each semicell (Illustrations of The Japanese Fresh-water Algae, 1977). Cell body slightly curved, gradually attenuated toward the truncated ends, which somewhat recurved due to the covexity of the inner margin near the ends; inner margin straight or slightly concave, outer margin convex, 300-500 μm long, 32-50 μm wide, L/W=9-14; cell wall smooth and colorless or sometimes delicately striated and yellowish-brown in color; chloroplasts with ridges containing 7-11 pyrenoids in central row (Photomicrographs of the Freshwater Algae, vol. 1, 1984).

50 μm 100 μm 150 μm; x 400 : 31 μm 63 μm 94 μm; x 640

Images of collecting locality: Kijioka Castle Ruin (Shiroyama park), Kodama, Honjo city (formerly Kodama town), Saitama Pref., Japan, April 15, 2006 by Y. Tsukii