Species [var. ralfsii]: Cell body slightly curved, swelled at the center, gradually attenuated (cf. C. kuetzingii, C. setaceum) toward both slanted and narrow ends (cf. C. rostratum), 300-610 μm long, (30-)40-62 μm wide, L/W=6-9; cell wall brownish in color, lined (7-9/10 μm); 6-9 pyrenoids in each semicell. [var. hybridum]: Cell body slender than var. ralfsii, slightly swelled at the center; 300-770 μm long, 24-40 μm wide, L/W=12-18. [var. gracilius]: Cell body smaller, narrower than var. ralfsii, 140-242 μm long, 11-25 μm wide. [var. novae-anguliae]: Cell body longe than var. ralfsii, (631-816)-1080 μm long, (23-26)-30 μm wide, L/W=28-31 (Illustrations of The Japanese Fresh-water Algae, 1977).

Similar species -->> C. kuetzingii; C. subulatum; C. rostratum;

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

Images of collecting locality: No. 5, Okahotto-Yatsu Museum (a biotope including rice field), Okahotto, Abiko city, Chiba Pref., Japan, February 17, 2008 by Y. Tsukii