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The structure of the frustule of vegetative cells of the diatom Cerataulus laevis Ehrenberg is described in detail. Reported for the first time is a fimbriate edge to the valve mantle. Sufficient morphological differences are noted to justify separation from the genus Biddulphia and the taxon is considered conspecific with Proteucylindrus Li et Chiang. The latter name therefore becomes an absolute synonym.
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Ehrlich et al. (1982) studied this question.
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