Symmetrical biraphid - Valves are elliptic to linear-elliptic with bluntly rounded ends. Partecta are all the same size. Striae consist of single rows of coarse areolae. Raphe branches are sinuous (not straight).
Mastogloia smithii var. grevillei
Symmetrical biraphid - Valve linear-lanceolate with apices protracted and rounded. The raphe is lateral, reverse lateral about midway from the apices to the central area. Striae are radiate and biseriate.
Symmetrical biraphid - Valves are linear-lanceolate to elliptic-lanceolate with subtly protracted and broadly rounded apices, lateral sterna, and partecta of two different sizes. The striae are uniseriate and the raphe is straight, rather than sinuous.
Symmetrical biraphid - Valves elliptic-lanceolate with protracted, broadly rounded apices. The raphe is filiform, becoming lateral at about ½ from the apices to the center. Striae are radiate and distinctly punctate.
Symmetrical biraphid - Valves linear-lanceolate, with margins slightly convex to nearly straight. The apices are bluntly produced. The raphe is straight and filiform, becoming lateral at about ½ the way between the apex and central area. The proximal raphe ends are enlarged. Striae are distinctly punctate and radiate, except at the apices where they are parallel.
Centric - Melosira undulata has large, robust, cylindrical frustules linked in long chains. Valves and mantles are conspicuously ornamented with rimoportulae and striae. A ring of evenly-spaced rimoportulae encircles the mantle near the valve/mantle interface. The mantle is unevenly thickened internally, giving an undulating appearance.
Centric - Cells cylindrical, often forming long chains. Valve face slightly convex, covered with very small spines. Unlike many Aulacoseira species, valves lack areolae.
Araphid - Valves linear-clavate, asymmetric to the transapical axis. Costae are present running transversely across the valves. A narrow sternum extends the length of the valve. A single rimoportula is located near the headpole.
Araphid - Valves are slightly heteropolar, with ovoid to linear-lanceolate margins. Frustules typically attach to one another in long ribbon-like colonies. Transapical costae are mostly perpendicular to the apical axis and number 4-6 in 10 µm. Striae are distinct and number 16-18 in 10 µm.