Abstract
The type material of the type species of Cyclotella, Cyclotella tecta Håkansson & Ross (syn. C. operculata auct., non (Ag.) Kütz.), has been investigated by light and electron microscopy and compared with the original material of C. distinguenda Hustedt and C. plitvicensis Hustedt, and also with other similar taxa. It is shown that C. tecta and C. distinguenda are conspecific and that the name C. distinguenda should be used for the taxon. C. plitvicensis, however, is a species in its own right.