An arrangement of four diatoms from Arroyo Hondo, Maria Madre Island, Mexico. Fossil marine material from the Miocene. Mounted in Naphrax and dated August 1969. The lower label says ‘see over’, but there was nothing on the other side…. Prepared by ECP Bone. Olympus BHB microscope using 450nm LED light. As well as the arrangement I imaged one using the 63x Leitz Pl Apo NA 1.4 objective, oil immersion. Olympus Aplanat Achromat condenser, oil immersion, oblique lighting. 2.5x Nikon CF PL photoeyepiece. Monochrome converted Nikon d850 camera. 58 images stacked in Zerene (Pmax).
I think this one is Biddulphia deodora (pentagonal form). Biddulphia deodora G.D.Hanna & W.Grant, 1926. Published in: Hanna, G.D. & Grant, W.G. (1926). Expedition to the Revillagigedo Islands, Mexico, in 1925, II. Miocene marine diatoms from Maria Madre Island, Mexico. Proceedings of the California Academy of Sciences, series 4, 15(2): 115-[193]. [in English]. Page 121, Plate 14, Figures 1,2.
Also see Amphipentas pentacrinus / Triceratium pentacrinus from Madagascar as this looks very familiar (see here).