Slide labelled as Porodiscus, from Forrester’s Hill, Oamaru. I’ll come back to the name in a minute. Single example on the slide. Dated 17/11/1946 and mounted in Styrax. No makers name, but based on style and handwriting I think this is by WF Reeve. Olympus BHB microscope using 450nm LED light. 63x Leitz Pl Apo 1.4 objective, oil immersion. Olympus Aplanat Achromat condenser, oil immersion, slightly oblique lighting. 2.5x Nikon CF PL photoeyepiece. Monochrome converted Nikon d850 camera. 82 images stacked in Zerene.
Back to the name. This certainly does have characteristics of Porodiscus. It does have features similar to P. hirsutus which is found in Oamaru. However to me it doesn’t look identical. Then there’s the cracks. They don’t look fresh to me (from the mounting of it). They look old. It made me think of Podosira superba var. reticulata from the Moreno shales (published in: Long, J.A., Fuge, D.P. & Smith, J. (1946). Diatoms of the Moreno Shale. Journal of Paleontology 20(2): 89-118, 2 figures, plates 13-19. Page 110, Plate 19, Figure 2.), which is screenshotted above. As I cannot find another one the same to compare with, for now it remains a bit of a mystery. Any thoughts please let me know.