Aloisalthella, a new genus of fossil Polyphysacean green algae (Chlorophyta, Dasycladales), with notes on the genus Clypeina (Michelin, 1845)

Following a preliminary historical survey of the Cenozoic Clypeina marginoporella Michelin, 1845, which is the type species of the respective genus, and of the Mesozoic Clypeina sulcata (Alth, 1882), the point was made that these two species may not be ascribed to the same genus. Accordingly, the new genus Aloisalthella is introduced with Clypeina sulcata as type-species. In addition, the generic diagnosis of Clypeina is amended (i.e., shortened) in order to exclude all features that are not present in its type, e.g., there are no verticils of sterile laterals inserted between successive verticils of fertile laterals. A rather large collection of algae was used to illustrate some key characteristics of these algal taxa as well as a few features rarely observed in C. sulcata.