Slide labelled Podosira maxima (although I think that name is wrong and this should be Podosira variegata). Single example on the slide. No makers name, but based on the handwriting and style I this is by HRS Williams. No mountant details or date. Olympus BHB microscope using 450nm LED light. 63x Leitz Pl Apo 1.4 objective, oil immersion. Olympus Aplanat Achromat condenser, oil immersion, brightfield lighting. 2.5x Nikon CF PL photoeyepiece. Monochrome converted Nikon d850 camera. 78 images stacked in Zerene (Pmax).
A bit more on the name. Initial searches for Podosira maxima did not produce anything which looked like this. I therefore went through Schmidt’s Atlas, and came across Podosira variegata (Schmidt’s Atlas, Plate 140, Figs 3 and 4-6) which looked very like this one on the slide. I did come across another couple of references to Podosira variegata;
It was reported as being present in Turtle Bay, California in: Additions to the Pliocene Fauna of Turtle Bay, Lower California, with a Note on the Miocene Diatomite, Leo George Hertlein, Journal of Paleontology, Vol. 7, No. 4 (Dec., 1933), pp. 439-441 (3 pages). However no pictures were given.
It was also discussed in: López-Fuerte, F.O.; Siqueiros Beltrones, D.A.; Altamirano-Cerecedo, M.d.C. Species Composition and New Records of Diatom Taxa on Phyllodictyon pulcherrimum (Chlorophyceae) from the Gulf of California. Diversity 2020, 12, 339. https://doi.org/10.3390/d12090339. Images are shown in Figure 8l-n but these are not stacked so show its appearance art different focus depths.
At the moment I am lacking good stacked images (or SEMs) of Podosira variegata to compare against, but I think the match with the description in Schmidt’s Atlas is sufficient to go with it as the name.