Aulacodiscus sp., from Palos Verdes, California, USA. Single broken example on the slide. Fossil marine material. Mounted in Hymount and dated April 1965. Prepared by ECP Bone. Olympus BHB microscope using 450nm LED light. It’s quite large so a 20x objective image shows the whole thing, but I also did a stack with the 40x Leitz Pl Apo 1.00 objective, oil immersion. Olympus Aplanat Achromat condenser, oil immersion, oblique lighting. 2.5x Nikon CF PL photoeyepiece. Monochrome converted Nikon d850 camera. 55 images stacked in Zerene (Pmax). I couldn’t get close enough to use the 63x Leitz.
As for potential names, the best I can do so far is Aulacodiscus cornutus from Schmidt’s Atlas Plate 170, Figure 2 (this is from Sendai, Japan) and also in Barron, John A., Late Miocene-early Pliocene Marine diatoms from Southern California, Palaeontographica Abteilung B Band 151 Lieferung 4-6 (1975), p. 97 – 170. (Plate 3 Fig 6) best match so far (from Newport, California). However I’m just leaving this with the species name for now.