This description is taken from what Krammer calls Pinnularia krookii . Outline linear with distinctly triundulate sides. Middle swelling is slightly broader than the swelling at the poles.
Ends are capitate, bluntly rounded.
Strongly variable, thin to broad, widened at axial area. Area often asymmetrical, almost to the margin of the valve. Raphe philiform and straight, not bent in middle. Central nodule distinct. Synonym Navicula krockii Grunow 1882, p 155, fig.