An arrangement of four Arachnoidiscus sp. from Kamischev, Russia. Mounted in Styrax, and dated 8/11/[19]40. Some debris present. No makers name, but I think this is by WF Reeve (but will leave it with a question mark for now). Olympus BHB microscope using 450nm LED light. As well as the arrangement I imaged the smaller one, second from the left, 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. 30 images stacked in Zerene (Pmax).
As for what these are, the best match currently is Arachnoidiscus antiquus, even though it is a little older than would be expected for Kamischev. Arachnoidiscus antiquus Barker & Meakin, 1944. Original description: Barker, J.W. & Meakin, S.H. (1945). New and rare diatoms. Journal of the Quekett Microscopical Club, Series 4, 2(1): 18-22, pl. 3-4. Page 18, Plate 3, Figure 2. I will leave them as Arachnoidiscus sp. for now though.