Navicula genovefae

Valves are linear to linear-lanceolate, with protracted, rostrate to sub-capitate, broadly rounded apices. Striae are radiate and curved, becoming nearly parallel at the apices. Striae are considerably less dense at mid-valve, and striae here are occasionally shortened. Areolae are dense and difficult to visualize under LM, except along the axial area at mid-valve, where individual areolae are less dense and can be discriminated. The axial area is very narrow and expands slight to a small, round central area. The raphe is straight with inflated proximal ends.

The specimens shown above conform to the type illustration and dimensions of Navicula genovefae Fusey 1951. Unfortunately, however, we were unable to obtain Fusey material (it was either lost or destroyed).

This taxon should be compared to Prestauroneis protractoides (Hust.) Liu and Kociolek 2015, as the two taxa have been confused in surveys in North America. The identity of this taxon, however, is also problematic to resolve. The lectotype specimen of N. protractoides Hust. is difficult to reconcile with the type illustration. Hustedt mentions an expanded mid valve ("Schalen linear in der Mitte konvexen Rändern” OR "medio convexis”) that is not present in the lectotype specimen. It appears that the illustration is not representative of the specimen, or the specimen selected as the lectotype is not of the taxon Hustedt intended. Alternatively, one could argue that there are two similar taxa on the Hustedt slide; resolution requires further work.

Note that a Parlibellus protractoides (Hust.) Witkowski and Lange-Bertalot 2000 is a homotypic synonym of P. protractoides.