An Auliscus sp. from Palos Verdes, Los Angeles, California. Single example on the slide. I’ll come back to the name in a minute. Mounted in Nirax and dated June 1995. Some mountant degradation. Prepared by RH Taylor. Olympus BHB microscope using 450nm LED light. 40x Leitz Pl Apo NA 1.00 objective, oil immersion. Olympus Aplanat Achromat condenser, oblique lighting, oil immersion. 2.5x Nikon CF PL photoeyepiece. Monochrome converted Nikon d850 camera. 20 images stacked in Zerene (Pmax). This is a small diatom, and I couldn’t get close enough to use the 63x Leitz Pl Apo, so resolution is limited.
As for the name, the slide has this as Auliscus propinquus, which while sort of similar is not correct (see here for an example of A. propinquus). I think it is probably Auliscus pruinosus. Auliscus pruinosus Bailey 1854. Published in: Bailey, J.W. (1854). Notes on new species and localities of microscopical organisms. Smithsonian Contributions to Knowledge 7(3): 1-15. Page 5, Plate 1, Figures 5-8.