Compare Stephanocyclus quillensis

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Cyclotella distinguenda has smaller valves, a lower stria density, and the central area covers 1/3 to 1/2 of the valve face. 
Stephanocyclus gamma has 1-2 distinct central fultoportulae, uniseriate striae, and the central area covers 1/2 of the valve face. 
Stephanocyclus meneghiniana has smaller valves, more distinct alveolae, and the central area covers 1/3 to 1/2 of the valve face.
Cyclotella agassizensis has smaller valves, a lower stria density and small, submarginal spines.