Symmetrical biraphid - Valves normally linear-lanceolate. Apices normally rostrate. Central area small, commonly asymmetric, elliptic to irregular in shape. Raphe generally straight, but kinked near the central area. Proximal raphe ends deflected in the same direction. Striae punctate, slightly radiate, becoming almost parallel near the apices.
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 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.
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 are elliptical-lanceolate. Apices are normally rostrate, but round in small cells. Central area is elliptic to polygonal in shape. Raphe is generally straight but with a median kink. Proximal raphe ends are expanded. Striae are slightly radiate, becoming parallel at the apices.
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 are elongated and linear-clavate. The head pole is attenuated and subrostrate. A single rimoportula is located distal from the head pole, near the widest part of the valve. Costae mostly primary, with occasional secondary costa. The sternum is narrow and may be difficult to distinguish.
Araphid - Valves are symmetrical and linear, with subcapitate to capitate ends. Costae measure 3.3-4.9 in 10 µm. Striae are visible in LM, but individual areolae are not resolved. The sternum is central and well-defined. Each valve has a single, sub-apical rimoportula.
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 clavate, with a rostrate headpole. Costae extend transversely across the valve. A single rimoportula is present near the headpole. The sternum is narrow.
Araphid - Valves are isopolar, but slightly irregular in shape. Valves are linear-lanceolate, to oval in smaller specimens. 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.
Symmetrical biraphid - Valves are small and lanceolate. Lyre-shaped depressions are present on each side of the central sternum. Striae are not visible in LM.