Navicula notha

Valves are lanceolate to linear-lanceolate with slightly drawn-out ends. Axial area is narrow, central area is small, rhomboid to elliptical. Proximal raphe ends are noticeably deflected to the primary side. Striae are radiate and bent at valve center, convergent at apices, 14-17 in 10 μm. There are 36-40 lineolae in 10 μm.

Note that this concept of Navicula notha is different from that presented in Krammer & Lange-Bertalot (1991) and Lange-Bertalot (1993, 2001) who distinguished N. notha and N. heimansioides. Most studied populations of N. notha from USA, including the type population from Virginia, had both relatively small specimens that fit Lange-Bertalot's concept of N. notha (length equal or less than 32 μm) and large specimens fitting the concept of N. heimansioides (length equal or greater than 30 μm). A morphometric study across several USA populations failed to reveal any breaks in distribution of size and striae density. SEM examination of large and small specimens from the type material did not show any ultrastructural differences. Therefore, we consider N. heimansioides to be a part of N. notha.