An arrangement of four diatoms labelled as Hyalodiscus stelliger (I’ll come back to this later, as this is wrong as far as I can tell). Prepared by Watson and Sons Ltd. Label says “Test in Balsam for 1/25th“. I presume this means it is mounted in Canada Balsam and for a 1/25th of an inch objective. 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. 11mm of the spacer to the camera removed. 54 images stacked in Zerene (Pmax). The images were quite low contrast, presumably due to the use of Canada Balsam as the mountant.
Ok, the name. This is labelled as Hyalodiscus stelliger. However it doesn’t look like Hyalodiscus stelliger (for example see here, also from Watson and Sons Ltd, and H. & M. Peragallo, Diatomées marines de France et des districts maritimes voisins, 1897, page 362). What this looks like to me is Podosira maxima. This is written about in Grunow 1879, pl.21, fig.2. Published in: Grunow, A. (1879). Algen und Diatomeen aus dem Kaspischen Meere. New species and varieties of Diatomaceae from the Caspian Sea, translated with additional notes by F. Kitton. Journal of the Royal Microscopical Society 2: 677-691, pl. 21. In this it one alternative name is given as Hyalodiscus maximus. This mistake is odd for a couple of reasons. One it is Watson and Sons Ltd, a well known slide maker. Second it is a test slide, as such it is extra important to ensure that the diatoms on the label match the ones on the slide. If anyone knows as to whether Hyalodiscus stelliger is an old name which encompassed Podosira maxima please let me know. So for now I am going with Podosira maxima for the diatoms on this slide.