Eupodiscus californicus f. bioculata (written as biocellata on the slide) from Santa Monica, California, USA. Single example on the slide. No makers name on the slide, but I understand this is by JA Long. Olympus BHB microscope 450nm LED light. 63x Leitz Pl Apo 1.4, oil immersion. Olympus Aplanat Achromat condenser, oil immersion, oblique lighting. 2.5x Nikon CF PL photoeyepiece. Monochrome converted Nikon d850 camera. 53 images stacked in Zerene (Pmax).
Eupodiscus californicus f. bioculata Schmidt in Schmidt et al., 1886. Original description: Schmidt, A. (1886). Atlas der Diatomaceen-kunde. Aschersleben, Commissions-Verlag Von Ludwig Siever’s Buchandlung. Series III (Heft 23-24): pls. 89-96. Plate 89, Figure 20.
For more discussion on diatoms like this, see here.