Pinnularia dariana

Valves are linear-lanceolate, barely triundulate, or slightly expanded at mid-valve. Apices are broad and rounded. The axial area is linear-lanceolate, 1/4-1/3 of the valve width and gradually widens into a poorly separated central area. The central area is wider in the primary valve side.

Striae are radiate in the valve center and slightly convergent at the apices. One longitudinal line crosses the striae approximately in the middle (between the central area and valve margin). This longitudinal line is formed by the edge of internal alveolae openings is usually clearly visible under LM. A second longitudinal line is very close to valve margin and is only occasionally distinguishable in LM. The raphe is lateral, with slightly expanded central ends and sickle-shaped terminal fissures.

Note the valve outline is variable; some valves, such as those illustrated by Schmidt (1876), have rather smooth margins, lacking undulations. The specimen of P. dariana illustrated in Patrick and Reimer (1966) is depicted with a smooth outline, as is the original illustration in Schmidt (1876). The majority of populations, however, are characterized by slightly triundulate valves.