Quite an interesting slide this one. Labeled as Frustule w/- Porodiscus interruptus, Craspedoporus elegans, from Forrester’s Hill, Oamaru, New Zealand. Single example on the slide. Mounted in Styrax/Aroclor, and dated 4/4/[19]71. Prepared by Richard Gosden. 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. Monochrome converted Nikon d850 camera. 46 images stacked in Zerene (Pmax) for the full stack. This is actually both valves, and the lower valve (which has a different appearance to the top half) was imaged using the last 9 images from the stack, and is also shown. I couldn’t get close enough with the 63x Leitz Pl Apo objective, so resolution is limited.
Porodiscus interruptus Grove & Sturt 1887. Published in: Grove, E. & Sturt, G. (1887). On a fossil marine Diatomaceous deposit from Oamaru, Otago, New Zealand. Part III. Journal of the Quekett Microscopical Club, Series 2 3: 63-78, pls 5, 6. Page 67, Plate 5, Figure 8. This name is currently regarded as a synonym of Sturtiella elegans (Grove & Sturt) Simonsen & Schrader. Source of Synonymy: Desikachary, T.V. & Sreelatha, P.M. (1989). Oamaru diatoms. Bibliotheca Diatomologica 19: [1]-330, including 145 plates. Plate 109, Figure 1. Upper part of the one on this slide.
It is also known as Craspedoporus elegans.
As mentioned in S&D on page 241, this diatom has 2 different looking valves. This slide shows both valves, one above the other, so is very nice. The lower part is something that has been on my wish list for a while, and I have just realized that is part of a dissimilar pair of valves, which helps with understanding the quite different names for this species.