Strew slide from Chesapeake Beach to Plum Point, Mid (Maryland), USA. Variety of species. Mounted in Naphrax and dated June 1975. Prepared by Bernard Hartley. Olympus BHB microscope using 450nm LED light. I chose an example of an Actinoptychus sp. for high magnification imaging. 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. 46 images stacked in Zerene (Pmax). Coverslip ring prevented me from using the 63x Leitz objective.
I think this is probably Actinoptychus senarius as it seems to be a good match. Interesting article on Jstor; Andrews, G. W. (1978). Marine Diatom Sequence in Miocene Strata of the Chesapeake Bay Region, Maryland. Micropaleontology, 24(4), 371–406. https://doi.org/10.2307/1485369. https://www.jstor.org/stable/1485369
Seems to be slide 694 Bernard Hartley’s Sample and Strew Slide Collection PDF (accessed from here). However this slide does not have an ID number so I can’t be certain.