Aulacodiscus sp. from Sendai (spelt Sandai), Japan. Single example on the slide, along with a girdle band. 8 processes. Reference to Schmidt’s Atlas Plate 158, Figure 2. Prepared by Laurence Miles. Olympus BHB microscope using 450nm LED light. 40x Leitz Pl Apo 1.00 objective, oil immersion. Olympus Aplanat Achromat condenser, oil immersion, oblique lighting. 2.5x Nikon CF PL photoeyepiece. 11mm removed from tube to the camera to increase the field of view. Monochrome converted Nikon d850 camera. 78 images stacked in Zerene (Pmax).
As for what this is I’ve shared another example, also from a Miles slide, here. As with that one, I am thinking this is Aulacodiscus nigricans, although it is larger than would be expected for that. Aulacodiscus nigricans Tempère & Brun 1889. Published in: Brun, J. & Tempère, J. (1889). Diatomées fossiles du Japon. Espèces marines et nouvelles des calcaires argileux de Sendaï et de Yedo. Mémoires de la Société de Physique et d’Histoire Naturelle de Genève 30(9): 1-75, pls 1-9. Page 20, Plate 4, Figure 1. Given the size issue, I am leaving it with a question mark though.
A really nice example.