An arrangement of seven Eupodiscus trioculatus (? var., more on this in a minute). Described as recent. No makers name but this is by Laurence Hardman. Olympus BHB microscope with 450nm LED light. Initial image with a 40x Leitz Pl Apo NA 1.00 objective, oil immersion. Main image (with the cropped diatoms) 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. 36 images stacked in Zerene (Pmax).
Ok, the name. Eupodiscus (trioculatus var.?) californicus‘) appears in: Van Heurck, H. (1882). Synopsis des Diatomées de Belgique. Atlas. pp. pls LXXVIII-CXXXII [78-132 and supplementary pls 22 bis, 82bis, 83bis, 83ter, 95bis], tables genres. Anvers: Ducaju et Cie. The image looks like a good match for this. There is also Eupodiscus trioculatus var. tricoculatus described in Greville, R. K. (1864). Descriptions of new and rare Diatoms. Series XIII. Transactions of the Microscopical Society, New Series, London. 12: 87-94. page(s): p. 88; pl. 12, fig. 3. As E. trioculatus var. trioculatus is a fossil specimen, and the ones on this slide are labelled as ‘recent’ I think the ones on the slide are likely Eupodiscus trioculatus var. californicus.