SUMMARYCulturing experiments are described in which the life cycles of several clones ofPhaeothamnion borzianum, a supposedly palmelloid form of the latter, andSphaeridiothrix compressaare investigated. The three types of algae turned out to be quite distinct taxa, not at all connected by intergrading forms as has been suggested in the literature. A new genus – to be namedTetrachrysis– is proposed to accommodate the taxon, formerly regarded as a palmelloid phase ofPhaeothamn