Triceratium peragalli from Sendai, Japan. Single example on the slide. Prepared by Arthur Cottam. Olympus BHB microscope using 450nm LED light. 40x Leitz Pl Apo NA 1.00 objective, oil immersion. Olympus Aplanat Achromat condenser, oil immersion, oblique lighting. 2.5x Nikon CF PL photoeyepiece. Monochrome converted Nikon d850 camera. 61 images stacked in Zerene (Pmax).
I think this is what is referred to in Schmidt’s Atlas as Triceratium peragalli forma. typica on Plate 167, Figure 3.