An arrangement of three Surirella sella from Joco, Chile. I understand these are fossil material. No makers name, but based on the style and handwriting, I think this was by JA Long. 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. 96 images stacked in Zerene (Pmax). These are a unusual shape, sort of like a saddle, but not aligned along the main axis, more at about 45 degrees to it.
Surirella sella Hustedt 1925. Published in: Schmidt, A.[W.F.] (1925). Atlas der Diatomaceen-kunde. Series VIII: Heft 91. pp. pls 361-364. Leipzig: O.R. Reisland. Plate 363, Figure 7.