A slide labelled as Navicula decussata from Victoria, Brazil. Single example on the slide. Prepared by JA Long and mounted in Sirax. There is quite substantial degradation of the mountant which can be see in the lower magnification image, and I have tried to clean this up as best I can for the main stack. Olympus BHB microscope using 450nm LED light. 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. 35 images stacked in Zerene (Pmax). I opened the condenser further than usual with this one (to about NA 1.2) and used a more oblique setting than usual as well. Some of the degraded mountant is visible in the top right of the diatom, but the structure of it is remarkably intact. Quite a beautiful diatom and best viewed using the zoom function.
I say ‘labelled as’ for this one, as I am not convinced about it being a Navicula. It looks more like a Pleurosigma of some type to me. N. decussata does not appear in Schmidt’s Atlas. It was published in Kützing, F.T. (1849). Species algarum. pp. [i]-vi, [1]-922. Lipsiae [Leipzig]: F.A. Brockhaus. But there is no picture in there. I found another potential name for it – Schizonema decussatum – published in Kuntze, O. (1898). Revisio generum plantarum. Vol. 3(3) pp. 1-576. Leipzig, London, Milan, New York, Paris: Arthur Felix, Dulau & Co., U. Hoepli, Gust. E. Stechert, Charles Klincksieck. But again no picture. So far I have been unable to find a an image of one to compare against. If you have one, drop me a message please.