Strew slide from Newport Beach (Mark 6X), California. Variety of species. Mounted in Aroclor and dated June 1975. No makers name but this is by Bernard Hartley. Olympus BHB microscope using 450nm LED light. I chose an example of a Stictodiscus sp. for high magnification imaging. 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. 20 images stacked in Zerene (Pmax). Underside view with the rim towards the coverslip.
I think this is probably Stictodiscus californicus Greville 1861. Published in: Greville, R.K. (1861). Descriptions of new and rare Diatoms. Series IV. Transactions of the Microscopical Society, New Series, London 9: 79-87, pl. X. Page 79, Plate 10, Figure 1.