Abstract
Original material of Campylodiscus clypeus (Ehrenberg) Ehrenberg ex Kützing, which is also the type of the name of the genus Campylodiscus Ehrenberg ex Kützing, was studied and a specimen has been selected to serve as lectotype. The size variation in two populations from two localities from two different times was analyzed. Because of its unusual habitat—a spring flowing out of a diatomite—the geology of the type locality is recapitulated and the taxon's published and unpublished distribution is recorded. This diatom is alive today occurring mainly in waters of higher conductivity but apparently had its peak in subfossil times at least at the type locality.