Slide labeled Aulacodiscus (excavatus ?) from Carlovo (also seen spelt Carlova). 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. 69 images stacked in Zerene (Pmax).
Based on Schmidt’s Atlas Plates 459 and 460, and the description therein, and the relatively large areolae on this diatom, I think it is likely to be Aulacodiscus excavatus var. robusta, but could possibly be A. excavatus, or even perhaps A. subexcavatus so will leave it with a question mark for now.
I recently acquired about 60 slides by this maker, 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.