Species [var. contractum]:
Cell body 28-41 μm long, 18-31 μm wide,
isthmus 5.3-8.7 μm wide, L/W=1.5; semicells broad ellipsoid, laterally circular;
cellwall smooth or finely dotted, a single pyrenoid in each semicell.
[var. ellipsoideum (Elfving) W. et G.S. West]:
Cell body 31-51 μm long, 24-42 μm wide,
isthmus 7-12.5 μm wide, L/W=1.3; apex of semicells slightly flattened; cellwall smooth.
[f. jacobsenii (Roy) W. et G.S. West]:
Semicells exactly ellipsoid, 28-47.6 μm long, 18-36.4 μm wide,
isthmus 4.5-11.3 μm wide.
[var. minutum (Delponte) W. et G.S. West]:
Cell body 19-28 μm long, 14-22 μm wide, isthmus 4.3-5.6 μm wide;
semicells elongated ellipsoid, laterally circular, cellwall dotted.
(Illustrations of The Japanese Fresh-water Algae, 1977).
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