Species [ var. ulna ]: Cell body slightly curved, both lateral margins parallel, slightly tapered toward ends, both ends broadly truncated, 170-(192-462)-500 μm long, 10- (11-22)-23 μm wide, L/W=15-20; cell wall brownish in color, striated (10-11/10 μm), bands present; 6-15 pyrenoids in each semicell. [ var. recurvatum ]: Thinner than var. ulna, recurved at both ends, 248-(298)-345 μm long, 9-11-(18) μm wide, L/W=30; cell wall smooth without striae (Illustrations of The Japanese Fresh-water Algae, 1977).

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