I think this is a Coscinodiscus of some type (or maybe a Podosira) from Haliotis Shells, California. Unknown slide maker, although it could well be Henry Morland. Mounted in Styrax, dated 14.2.1920. Olympus BHB microscope using 450nm LED light. 40x Leitz Pl Apo NA 1.00 objective, oil immersion. Olympus Aplanat Achromat, oil immersion, brightfield lighting. 2.5x Nikon CF PL photoeyepiece. Monochrome converted Nikon d850 camera. 22 stacked in Zerene (Pmax).