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Abstract:
Information is presented on the morphology of several epipelic naviculoid diatoms which can occur abundantly on stream sediments. In each case allocation to "well-known" described species is to some extent unsatisfactory, particularly in the light of published ecological preferences. Their inclusion in loosely defined, widely distributed species is rejected. The necessity of recognising smaller ecologically distinct taxa is discussed, since without such treatment ecological information will be lost and bioindicator system will be unworkable. The species considered include Navicula capitata sensu lato, N. subcostulata, N. protracta and N. protractoides, N. gregaria, and N. rhynchocephala. Further taxonomic work is necessary to establish whether some of the variants should be described as new species or can be accommodated within existing taxa.
