The separation of Aulacoseira from Melosira C. Ag. in 1848 by Thwaites is substantiated with new light and electron microscope observations. Differences between the two genera concern the habitat, position of the nucleus, valve and girdle-band structure and, in Aulacoseira, lack of rimoportulae but presence of a distinctive type of tube-process for which the term carinoportula is proposed. Nomenclatural changes include the following new combinations: Aulacoseira epidendron (Ehrenberg) Crawford, A. dendrophila (Ehrenberg) Crawford, A. dendroteres (Ehrenberg) Crawford and A. circularis (Ehrenberg) Crawford.
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Richard M. Crawford (1981) studied this question.
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