Bit of a mystery this one. The slide is labelled as Mastogloia from Allan’s Farm, Oamaru, New Zealand. Single example on the slide. Fossil marine material. Mounted in Naphrax and dated June 1967. 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. 38 images stacked in Zerene (Pmax).
Back to the name. The label says Mastogloia, but I couldn’t find a visual match with any Mastogloia from Oamaru. It looks more like a Dictyoneis of some type to me. Indeed in: Schrader, H.-J. (1969). Die Pennaten Diatomeen aus dem Obereozän von Oamaru, Neuseeland. Beihefte zur Nova Hedwigia 28: 1-163, pls 1-39. Page 42, Plate 19, Figure 7 there is an image of something which looks similar to this, and Schrader also described it as a Dictyoneis of some type. It remains a bit of mystery for now.