Genus: Colonies of a fixed number of cells, flat, circular in shape; cell body polygonal in shape, with horn-like projections; cell wall garanulated, wrinkled or notched; chloroplasts plate-like or reticular; asexual reproduction by zoospore; sexual reproduction by isogametes (Illustrations of The Japanese Fresh-water Algae, 1977). Species: Colonies of 8, 16, 32, 64 cells, without perforations; basal parts of the marginal cells polygonal, usually 4- to 5-sides; outer sides concave, incision V- or U-shaped, with two conical processes; cell wall with irregularly reticulate ridge (Photomicrographs of the Freshwater Algae, vol. 18, 1997).

Simiar species -->> P. duplex var. rugulosum (with perforations);

31 μm 63 μm 94 μm; x 640