Thalassiosira rotula. Prepared by RI Firth. Three examples of the diatom on the slide in a linear arrangement. No date or mountant specified. The notes on the slide say ‘Podosiria ?’ at the top and ‘Porosira glacialis (Grunow) E. Jørgensen or Thalassiosira rotula Meunier‘ at the bottom. I think this looks more like T. rotula so have gone with that as the name. Olympus BHB microscope using 450nm LED light. 63x Leitz Pl Apo NA 1.40 objective, oil immersion. Olympus Aplanat Achromat condenser, oil immersion, oblique lighting. 2.5x Nikon CF PL photoeyepiece. Monochrome converted Nikon d850 camera. 26 images stacked in Zerene (Pmax).