Eunotia incisa

The ventral margin is straight in smaller specimens and weakly concave in larger specimens. The dorsal margin is convex. The apices are acutely rounded, appearing 'nose-like' due to the inset position of the helictoglossae. The helictoglossae are set in equidistant from the apices (symmetric to the transapical axis), giving the appearance of an indentation in the LM. One apical rimoportula is present, just dorsal to the center of the apex, and is expressed externally as a round pore. The distal ends of the raphe lie on the valve mantle and the terminal raphe nodules are well set in from the apices. In girdle view the frustules are rectangular to quadratic and the inset helictoglossae are observable.

Several forms and variations in length (L), width (W) and stria density are currently included in the broad concept of E. incisa as presented by Patrick and Reimer (1966; L 15-50 µm, W 4-7 µm, 13-17 stria/10 µm), Krammer and Lange-Bertalot (1991, 13-50 µm, W 4-6 µm, 12-17 stria/10 µm), Siver et al. (2005, L 12-28 µm, W 3-4 µm, 16-17 stria/10 µm; also narrow specimens W 2-2.5 µm), and Furey et al. (2011, 13-50 µm, W 2.8-5.0 µm, 12-17 stria/10 µm). Some of the narrow specimens have been described as new species, such as E. canicula. Specimens that have broader, more rounded apices, such as valves similar in form to Taf. 161, Figs 13-15 in Krammer and Lange-Bertalot (1991) may later be described as new species, but for now should be tracked as a variation in valve form. Lange-Bertalot et al. (2011) have further described new species from Europe, such as E. incisadistans, that share similarities in form (including the inset helictoglossae) that should be compared with the North American flora as taxonomic work on this species continues. Eunotia incisadistans has broader valves with lower stria density.