|  Species [var. costatum]: 
Cell body medium in size, inner side straight, outer side strongly convex, both termini conical, 
200-(304-385)-550 μm long, (28-41)-70 μm wide, 
L/W=6-8; cell wall brownish in color, 
striae separated each other (5-6 within 10 μm), ridged at both termini; 
chloroplasts with 5-6 laminae, 6-8 pyrenoids in each semicell. [var. westii]: 
Cell body more elongate, curved, 230-(336-480) μm long, 23-(30-43) μm wide, 
L/W=8-11; striae thin at the center, thick at both termini; small dots present between the striae  
(Illustrations of The Japanese Fresh-water Algae, 1977).
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