Rhaphoneis sp. (spelt Rhaponeis on the slide), Santa Monica. Single example on the slide. No makers name, but the handwriting would have this as being prepared by Frederick Marshall. 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. 31 images stacked in Zerene (Pmax).
Is this a Rhaphoneis, or is a Cocconeis, I’m not sure. If you have any strong thoughts about it please let me know.