| Popis: |
Ten species, six of which were previously placed in the genus Fragilaria, were examined, mainly by electron microscopy. Fragilaria germainii Reichardt and Lange-Bertalot is transferred to Diatoma, and Fragilaria alpestris Krasske is transferred to Staurosirella. In Fragilaria capucina Desmazières, one or two rimoportulae are present. In Staurosirella, new details are added concerning the structure of the aerolae; externally, they are multiseriate. Staurosirella pinnata (Ehrenb.) Williams and Round shows an original feature: internal "bridges," perforated by very tiny pores, together join the striae placed on each side of the sternum; moreover, these pores give a particular structure to the striae. In Staurosirella leptostauron (Ehrenb.) Williams and Round, the valvocopula is a closed band with a septum, which is new for this genus. Several species show spinose and nonspinose valves; consequently the presence or the lack of spines does not seem to be an appropriate criterion to distinguish two species. |
