A slide labelled as Actinoptychus, from Newport, California. Single example on the slide. Mounted in Styrax. No makers name, but this is by JA long. I’ll come back to a potential name in a minute.
Olympus BHB microscope using 450nm LED light. 63x Leitz Pl Apo 1.4 objective, oil immersion. Olympus Aplanat Achromat condenser, oil immersion, oblique lighting. 2.5x Nikon CF PL photoeyepiece. Monochrome converted Nikon d850 camera. 66 images stacked in Zerene (Pmax). The central region shows some nice structure which is easier to see when isolated and the contrast boosted.
Back to the name. It seems the maker presumably wasn’t sure about it, which is why it was left as ‘Actinoptychus‘. Looking in “Wornardt, W.W., Jr. 1967. Miocene and Pliocene marine diatoms from California. Occasional Papers of the California Academy of Sciences 63:108 pp.” it looks to me like the one in Figure 72 which is labelled as an example of Actinoptychus splendens var. angelorum, hence I am going with that but keeping the question mark after the name.