Typification of Cocconeis lineata and Cocconeis euglypta (Bacillariophyta)

The nominate varieties of the monoraphid diatoms Cocconeis lineata Ehrenberg and C. euglypta Ehrenberg are typified. Lectotypes of both taxa are preserved at the Ehrenberg Collection, Museum fur Naturkunde, Berlin, Germany. The lectotype of C. lineata is a poorly detailed drawing, showing an ovoid valve (or frustule?) with two to three apical lines on each hemivalve. The lectotype of C. euglypta, contained in a mica, shows a unique, broadly elliptical sternum valve with up to five apical striae on each hemivalve, displaying a zigzag pattern. This is roughly consistent with the current concept of C. lineata and C. euglypta and with their usage over the last 160 years. To ensure stabilization of the names and current concepts for these two taxa, culture-based epitypes of C. lineata and C. euglypta are designated. Light and electron microscopy observations, as well as morphometric data from clones for both taxa, are presented and an amended description for each taxon is provided.