Two Aulacodiscus sp., from Troublesome Gully, Oamaru, New Zealand. Described as A. rattrayii, but I’m not convinced by this, more in a minute. Fossil marine material from C. Swatman. Mounted in Canada Balsam and dated September 1967. Severely damaged coverslip with extensive cracks. Prepared by ECP Bone. 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. 67 images stacked in Zerene (Pmax).
As for the name. The slide has them as A. rattrayii. However with A. rattrayii the processes are further in from the edge than these. Looking through the Oamaru Diatoms website, and Desikachary and Sreelatha’s book on Oamaru diatoms, the closest I can find would be Aulacodiscus comberi.