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Rotational symmetry of cell face outline is 360 degrees ; one end is a reflection of the other (but the halves are not), i.e. semi-circular or crescent shaped
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Boat-shaped to slightly curved in valve view; raphes present on both valves (visible by fibulae), lying along the same side of the cell (vs. opposite sides in Nitzschia); striae fine.
Hantzschia
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Both valves visible in girdle view, because girdle is narrower on one side; raphes do not cross the valve faces (and are difficult to see, along one edge of the valve); cell poles are curved and pointed in valve view, with a bulge in the opposite direction at the midpoint.
Rhopalodia
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Both valves visible in girdle view, because girdle is narrower on one side; raphes cross the valve face in the centre, forming an arch; "Napoleon's hat" shape in valve view.
Epithemia
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"Orange segment" shape in valve view; raphes on both valves; raphe ends turn towards the long edge of the valve.
Cymbella
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Curved in valve view, maybe with protruberances or swellings; each valve has a short raphe at each end, which curves from the side of the valve face onto the face (difficult to see).
Eunotia and relatives
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"Orange segment" shape in valve view; raphes on both valves, approx. parallel to the short edge of the valve, and turning towards the short edge at the ends (vs. Cymbella).
Encyonema
