Cosmarium obsoletum (Hantzsch) Reinsch 1867

    Cells medium sized, 1.2 times longer than broad measures 42–48 µm in length and 49–54 µm in width. Cells deeply constricted at the center, sinus closed excluding the inside, isthmus is 17–21 μm. Semicell depressed semi-circular, convex or truncated apex, basal angle thick and blunt stout. Semicells circular in lateral view and elliptical in vertical view; protrudent apex and cell wall shows sparsely punctate.