|  Species [ var. connatum ]: 
Cell body 22-24 μm long, 
19.6-25 μm wide (excluding spines), isthmus 7-9 μm wide; 
spines short; semicells inverted semicircle in shape, apex flat or slightly convex. [ var. pseudamericanum Grönblad ]: 
Cell body larger than v. connatum 39-45 μm long, 
25-36.45 μm wide (excluding spines), isthmus 5.6-11 μm wide; 
corners of semicells protruded upward making its apex concave.
 [ var. rectangulum Roy et Bisset ]: 
Cell body 14-20 μm long, 14.7-20 μm wide (without spines), 
isthmus 3.5-5.6 μm wide; side margins of semicells not convex; spines longer and 
thicker than v. connatum 
(Illustrations of The Japanese Fresh-water Algae, 1977)
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