Slide labelled as Campylodiscus latus from Jackson’s Rock, Oamaru. I think this name is incorrect, and that it should be Melosira praeclara. No makers name. 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).
Back to the name. The slide was labelled Campylodiscus latus. I wasn’t able to find reference to Campylodiscus in Oamaru, which got me looking for similar things. This led me to Melosira and in particular M. praeclara as shown in (Desikachary and Sreelatha, Plate 79, Figs 2 and 7). Synonymised name: Lysigonium praeclarum (Schmidt in Schmidt et al.) Kuntze, 1898.
This one has a certain simplistic beauty about. Visually it looks almost completely circular. Makes me think of the story of Giotto drawing a perfect circle for Pope Benedict XI to demonstrate his skill.