Subgenus: Eucosmarium
Genus: Unicellular; variable in shape; a constriction at the center of the cell body; mostly longer than wide; flattened; each semicell hemispherical, spherical, ellipsoidal, rectangular, pyramidal or kidney-shaped; no apical indentation.
Subgenus:Cell body dorso-ventrally compressed, with strong constriction at the center, transverse section elliptical or diamond-shaped (Illustrations of The Japanese Fresh-water Algae, 1977).
| Section Quadratiformes: Cell surface smooth or dotted or punctated; semicells rectangular | |||
C. quadratum 10 samples 50-80 x 30-40 μm 2003-2008 |
C. rectangulare 4 samples 36-42 μm 2004-2005 |
C. angulosum 8 samples 14-40 μm 1999-2008 |
C. pseudobinerve 2 samples 44 x 25 μm 2006-2008  |
C. norimbergense v. norimbergense 17 x 14 μm Kurihashi Saitama, 2001 |
C. norimbergense v. depressa ? 12 x 11 μm Tochigi, 2000 |
C. pseudoexiguum 6 samples 18-26 μm 2003-2007 |
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