Coscinodiscus heteroporus from Kamischev, Russia. Single example on the slide mounted with the rim towards the coverslip (presumably this is an ‘underside view’). Mounted in Styrax and dated 20/11/[19]65. Prepared by CN Walter. 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. 24 images stacked in Zerene (Pmax).
Coscinodiscus heteroporus Ehrenberg 1844. Published in: Ehrenberg, C.G. (1844). Untersuchungen über die kleinsten lebensformen im quellenlande des Euphrats und Araxes, so wie über eine an neuen formen sehr reiche marine tripelbildung von den Bermuda-Inseln. Bericht über die zur Bekanntmachung geeigneten Verhandlungen der Königlich-Preussischen Akademie der Wissenschaften zu Berlin 1844: 253-275, 1 pl. Page 265.
Also see the mention in: Geology and biology of North Atlantic deep-sea cores between Newfoundland and Ireland, Part 3, Diatomaceae, Professional Paper 196-B, by: K. E. Lohman, https://doi.org/10.3133/pp196B. Page 70.