Observations on Bellerochea and Streptotheca, including descriptions of three new planktonic diatom species - Stosch, H.A. von (In: R. Simonsen (ed.), Proceedings of the Fourth Symposium on Recent and Fossil Marine Diatoms, Oslo, August 30 - September 3, 1976. Beihefte zur Nova Hedwigia, 1977)