Eupodiscus oculatus from Santa Monica. Single example on the slide. Described as ‘very rare’. Prepared by Arthur Charles Cole. Olympus BHB microscope using 450nm LED light. 63x Leitz Pl Apo 1.4 objective, oil immersion. Olympus Aplanat Achromat condenser, oil immersion, slightly oblique lighting. 2.5x Nikon CF PL photoeyepiece. Monochrome converted Nikon d850 camera. 45 images stacked in Zerene (Pmax). View from the underside with the rim facing the coverslip.
A note now about the name. The slide has it as Eupodiscus oculatus. It is shown in Schmidt’s Atlas Plate 117, Fig 9, where it is described as; “Monterey, Eupodiscus oculatus Grev.; vielleicht richtiger unter Pseudauliscus zu stellen.”. Translated as “Monterey, Eupodiscus oculatus Grev.; perhaps more correctly placed under Pseudauliscus.”. I understand this is now called Pseudauliscus oculatus (ref: Sims, P.A. (2001). The genus Praetriceratium gen. nov.: a survey of eupodiscoid genera with a sipho marginalis. Diatom Research 16(2): 399-416.). Thing is there is another diatom which looks very similar to this – Eupodiscus californicus f. bioculata (which is shown in Schmidt’s Atlas on Plate 89, Fig 20). I have described a couple diatoms on this site as this as they looked to more like it than Eupodiscus oculatus based on Schmidt’s images (for example here and here). Now I have an example of Eupodiscus oculatus does this change my opinion? With this one the ‘eyes’ look to be closer together (further from the edge) and perhaps more round, than the other 2 examples. Is this enough to make them different? Not sure. Overall I think that Eupodiscus oculatus (Pseudauliscus oculatus) and Eupodiscus californicus f. bioculata are very similar and could perhaps be descriptions of the same diatom, however more work would be needed to confirm that. Whatever the name, a very good looking diatom.