Guide to Brachysira brebissonii

Valves are rhombic-lanceolate to elliptical-lanceolate in valve outline. Striae are weakly radiate across the entire valve face. The raphe is positioned within two external ribs on the valve face. The ribs terminate at the edge of the central area and the apices. The areolae are irregular in shape and spacing, creating a “wave-like” appearance of the striae. The orientation and size of areolae, creates a series of wavy longitudinal hyaline zones. Central area is small and circular to slightly oval. Valves may vary in the development of external ribs.