Actinoptychus sp. from Palos Verdes, California, USA. More on the name in a minute. Single example on the slide. Mounted in Zrax and dated August 1993. Prepared by RH Taylor. Olympus BHB microscope using 450nm LED light. 20x Nikon Plan Apo NA 0.65 objective. Olympus Aplanat Achromat condenser, oblique lighting. 2.5x Nikon CF PL photoeyepiece. Monochrome converted Nikon d850 camera. 24 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. Also it was lower that expected contrast.
Right, the name. The slide says Actinoptychus ‘tribunatus’. As far as I can tell there is no such thing. Looking through Schmidt’s Atlas it maybe Actinoptychus gründleri f. minor (Plate 100, Figure 4), but that is a somewhat tentative ID.