Knetodiscus aculeiferus, no details on mountant or location. Slide label says Pyxilla or Pterotheca. Single example on the slide. Unknown maker. 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. 65 images stacked in Zerene (Pmax).
After speaking with an expert, this is an example of what would have previously been known as Pterotheca aculeifera. However it would now be know as Ktenodiscus aculeiferus (Grunow) S.Blanco & C.E.Wetzel, 2016. See: Blanco, S.; Wetzel, C. E. (2016). Replacement names for botanical taxa involving algal genera. Phytotaxa. 266(3): 195.
I recently acquired about 30 more slides by this maker to add to the ones I already had, so if you want to see others by them, search for AAAAA in the Search option at the top of the page, and I’ll include this in each of the pages for them.