Cosmarium quadrum P. Lundell 1871

    Cells medium sized, quadrate in shape, as long as broad or slightly longer measures 40–71 µm in length and width is 35–65 µm. Cells deeply constricted, sinus narrowly linear, with a slightly dilated proximal end, isthmus 14–18 µm. Semicells sub-rectangular with rounded basal angles and sides slightly convex or slightly straight, apex rounded or slightly truncate. Semicell subcircular in lateral view and oblong -elliptic in vertical view. Cell wall covered densely with big and blunt granules.