Navicula rostellata

Valves are linear to linear-lanceolate with slightly convex (more typically) to straight margins and subrostrate apices. The axial area is narrow and straight. The central area is elliptic and slightly asymmetric. The raphe is straight, with external proximal raphe ends that are slightly dilated and bent toward the primary side of the valve. The central nodule is asymmetrically expanded on the internal valve surface to the primary side. Terminal raphe fissures are hooked to the secondary valve side. Striae are bent and radiate around the center. The striae are more distant from one another near the center of the valve, 12-14 in 10 µm. The striae become parallel, then convergent at the apices. The areolae are usually visible under LM and number around 30 in 10 μm.

Note that the original material of Navicula rostellata has not been investigated. As Patrick (Patrick and Reimer 1966) pointed out, the identity of this taxon is not clear as the original illustration shows a linear valve outline and long, narrow apices. Patrick and Reimer (1966) illustrated a specimen from Bengal with linear valve outline and low stria density (9-10 striae in 10 µm) as N. viridula var. rostellata. The concept we present in this page follows Lange-Bertalot (2001).