A strew from the Antarctic (although not written on this label, other slides which I got at the same time from the same source said the Antarctic material was provided by NBS – Northern Biological Supplies). Washed sample in Naphrax and dated 1-3-[19]39. Some issues with the mountant. No makers name. Olympus BHB microscope using 450nm LED light. As well as the strew, I imaged a Corethron sp. (maybe C. pennatum) using the 20x Nikon Plan Apo objective and oblique light. I also did some high magnification images using the 63x Leitz Pl Apo 1.4 objective, oil immersion. Olympus Aplanat Achromat condenser, oil immersion, oblique lighting. 2.5x Nikon CF PL photoeyepiece. Monochrome converted Nikon d850 camera. Images stacked in Zerene (Pmax).
I’m going with Corethron pennatum (Grunow) Ostenfeld, 1902. Published in: Ostenfeld, C.H. (1902). Marine plankton diatoms. In: Flora of Koh Chang. Contributions to the knowledge of the vegetation in the Gulf of Siam by Johs. Schmidt. Part VII. Botanisk Tidsskrift 25(1): 219-245, 23 figures. Page 224.
Also see: Richard M. Crawford, Friedel Hinz & Claire Honeywill (1998) Three species of the diatom genus Corethron Castracane: Structure, distribution and taxonomy, Diatom Research, 13:1, 1-28, DOI: 10.1080/0269249X.1998.9705432.