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). Species (var. antilopaeum) : Cell body 45-72 μm long, 43-71 μm wide, L/W = 1, constriction 13-25 μm wide, spines 19-22 μm long, semicells with 4 spines (2 anterior, 2 basal), cell wall at the center of semicells thickened and punctated (Illustrations of The Japanese Fresh-water Algae, 1977).

31 μm 63 μm 94 μm; x 640

Images of collecting locality: Dojo-ike (pond), Norikura highland, Azumi, Matsumoto city (formerly Azumi village), Nagano Pref., Japan, June 8, 2006 by Y. Tsukii

X. antilopaeum (Brébisson) Kützing var. antilopauem: Cell body 45-72 μm long, 43-71 μm wide, L/W = 1, constriction 13-25 μm wide, spines 19-22 μm long, semicells with 4 spines (2 anterior, 2 basal), cell wall at the center of semicells thickened and punctated (Illustrations of The Japanese Fresh-water Algae, 1977).

X. antilopaeum var. laeve Schmidle: Cell body 79-90 μm long, 62-79 μm wide, constriction 20-34 μm wide, spines 19-22 μm long, semicells with 4 spines (2 anterior, 2 basal), cell wall at the center of semicells without thickened and punctated (Illustrations of The Japanese Fresh-water Algae, 1977).