Auliscus sp. (I am fairly sure this is Auliscus speciosus) from Palos Verdes, California, USA. Single example on the slide. Mounted in Irax II (?) and dated August 1993. Olympus BHB microscope using 450nm LED light. 50x Leitz Fluoreszenz NA 1.00 objective, water immersion. Olympus Aplanat Achromat condenser, oil immersion, oblique lighting. 2.5x Nikon CF PL photoeyepiece. Monochrome converted Nikon d850 camera. 32 images stacked in Zerene (Pmax). A slightly frustrating slide. I would normally have used the 40x Leitz or 63x Leitz Pl Apo objective, however I couldn’t get close enough with either, which makes me think it was mounted quite deeply.
Back to the name I am fairly sure this is Auliscus speciosus A. Schmidt in Schmidt et al., 1882. Original description: Schmidt, A. (1882). Atlas der Diatomaceen-kunde. Aschersleben, Commissions-Verlag Von Ludwig Siever’s Buchandlung. Series II (Heft 20): pls. 77-80. Plate 80, Figure 5. There is another example of this species on my site (here).