Genus: Variable in shape; strong constriction at center; semicell ellipsoidal, polygonal, etc.; cell wall with simple or branching spines, most of them laterally aligned; 4 plate-like chloroplasts in each semicell; one or more pyrenoids in each chloroplast (Illustrations of The Japanese Fresh-water Algae, 1977).

X. cristatum x 640	Xanthidium sp. x 640