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5; Hustedt, 1930, p. 789, Fig. 461; Cupp, 1943, p. 150, Fig. 108; Hendey, 1964, p. Ill, Plate 6, Fig. 6; Hasle, 1975, Figs. 149-151;Takano, 1979; von Stosch, 1980; von Stosch, 1987, p. 42, Figs. 46-59; Takano, 1990, pp. 298-299.

Generic characters:

Cells solitary or in ribbons.

Cells in girdle view rectangular to square.

Cells in valve view triangular, rarely biangular or quadrangular.

Marginal ridge membraneous.

Each valve with a central bilabiate process with long external tube.

Valve face with radial rows of poroid areolae starting from a nonperforated area around the process. Conspicuous elevations at valve corners.

Proximal to each elevation a depression in valve face across the corners. Chloroplasts, numerous small bodies.

Characters showing differences between species: Solitary or in ribbons.

Direction of marginal ridge in relation to valve mantle.

Structure of marginal ridge.

Shape of valve mantle.

Height of elevations.

Size of valve areolae.

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