Slide label as Triceratium but I think this is an Entogoniopsis sp.. Single example on the slide, tipping away from the coverslip towards the upper right. No location or makers name, but based on the style and handwriting this is by James Doke MacPhail. Also J.T.N.T. and 1903 on the lower label. 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. 128 images stacked in Zerene (Pmax).
As to the specific species I am not sure. There are small circular ‘unperforated areas’ in the middle of each polar elevation (similar to Entogoniopsis major, but this does not look like E. major). Areas just inside the polar areas are elevated compared with the central zone of the valve. An interesting diatom.