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' 3-4 fim in the middle of the valve, 1.7-2.7 /im at the ends, 1.3-2.0 pm in the narrow parts close to the valve ends (Hasle 8c Mendiola, 1967); Hallegraeff (1986) gives 400 /am as the maximum length and 5.5-10 areolae in 10 /am. ' Greater number closer to the apices.

' The maximum length is after Hustedt (1959); Hasle &c Mendiola (1967) measured 10-70 /am. d—, No data.

' 3-4 fim in the middle of the valve, 1.7-2.7 /im at the ends, 1.3-2.0 pm in the narrow parts close to the valve ends (Hasle 8c Mendiola, 1967); Hallegraeff (1986) gives 400 /am as the maximum length and 5.5-10 areolae in 10 /am. ' Greater number closer to the apices.

' The maximum length is after Hustedt (1959); Hasle &c Mendiola (1967) measured 10-70 /am. d—, No data.

Generic characters:

Cells in girdle view rectangular.

Cells isopolar or heteropolar.

Cells in valve view varying from smoothly dilated in the center (acicular, spindle shaped) to linear, or distinctly dilated in the center and at the apices, or one apex rounded and the other slightly tapering.

Sternum wide.

One marginal row of areolae.

Areolae circular.

Internal openings (foramina) of the areolae smaller than the external openings (SEM).

External openings of areolae crossed by a simple silicified bar (strut) or a pattern of crossing bars (struts; Plate 56; SEM). The simple bar is usually coarse and may be discerned with LM, whereas the more complicated pattern is delicate and is only occasionally and partly discernible with LM.

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