Abstract
It was proved by SEM observations that the valvocopula of the diatom Denticula tenuis var.crassula was composed of three cingular elements, namely bisegmented valvocopulae having traces of septa and septum-like plate, and some crossbars. It seems to be the most probable based on the microstructure of valve and girdle that the genus Denticula seas. str. is a heterogeneous taxon including at least two ancestries. The one is the group distributed in Sumatra and its vicinities having the constructions, for instance raphe system, pore occlusion and valvocopula etc., in common with the genus Epithemia BRÉB.. The other is the group which is close related with the section Fragilariopsis of Nitzschia HASSALL and Nitzschia valdestriata AL. et HUST..
