An arrangement of three Stictodiscus hardmanianus from Jackson’s Paddock, Oamaru, New Zealand. The two smaller ones are quite tilted (hence the more oval appearance). Prepared by William Allott Firth. Olympus BHB microscope using 450nm LED light. The larger one was imaged at high resolution with a 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. 52 images stacked in Zerene (Pmax).
Stictodiscus hardmanianus Greville 1865. Published in: Greville, R.K. (1865). Descriptions of new and rare diatoms. Series XVII. Transactions of the Microscopical Society, New Series, London 13: 97-105, 2 pls [VIII, IX]. Page 98, Plate VIII, Figure 4.
I suspect the 2 smaller ones are Stictodiscus hardmanianus var. hardmanianus, while the larger one is either Stictodiscus hardmanianus var. hardmanianus or Stictodiscus hardmanianus var.megapora (note the difference in the appearance of the central regions in the 20x image).