A slide labelled as Stephanogonia or Mastogonia polygonia. From Szakal, Hungary. Two examples on the slide. No name for the preparer. The slide label wasn’t the easiest to read, but there is reference to Stephanogonoia polygonia in Proceedings of the Boston Society of Natural History, Vol XI, 1868, page 79. In Elisabeth Fourtanier & J. Patrick Kociolek (1999) CATALOGUE OF THE DIATOM GENERA, Diatom Research, 14:1, 1-190, DOI: 10.1080/0269249X.1999.9705462, on page 88 it is mentioned that “Peragallo [1897] placed some of the original species of Ehrenberg into synonymy with Mastogonia crux, treated the other species as belonging to the genera Pyxidicula and Stephanogonia, leaving in the genus Mastogonia only Mastogonia crux.”. It appears that around the end of the 1800s these names were in flux, and this is likely the date of the slide.
Olympus BHB microscope using 450nm LED light. Individual images done using a 63x Leitz Pl Apo NA 1.40 objective, oil immersion. Olympus Aplanat Achromat condenser, oil immersion, brightfield lighting. 2.5x Nikon CF PL photoeyepiece. Monochrome converted Nikon d850. Images stacks prepared in Zerene (Pmax).