Entogonia davyana from Barbados. Single example on the slide. Mounted in Canada Balsam. Prepared by John Andrew Shulze, Philadelphia (see here for more details). Olympus BHB microscope using 450nm LED light. 63x Leitz Pl Apo 1.4 objective, oil immersion. Olympus Aplanat Achromat condenser, oil immersion, slightly oblique lighting. 2.5x Nikon CF PL photoeyepiece. Monochrome converted Nikon d850 camera. 68 images stacked in Zerene (Pmax).
See review: Holmes, R.W. & Brigger, A.L. (1979). The marine fossil diatom genus Entogonia Greville – A review. Bacillaria 2: 155-214. Personally, I think it looks like it could potentially be E. davyana var. intermedia, so will leave that with a question mark for now.