Arachnoidiscus cognatus from Barbados. Single example on the slide. Mounted in Aroclor and dated 13th February 1992. Coverslip 0.11mm. Prepared by Peter C Finch. 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. 43 images stacked in Zerene (Pmax).
Arachnoidiscus cognatus N.E.Brown 1933. See: Brown, N.E. (1933). Arachnoidiscus. An account of the genus, comprising its history, distribution, development and growth of the frustule, structure and its examination and purpose in life, and a key to and descriptions of all known species, illustrated. W. Watson & Sons, Ltd., London., 88 pp., 7 pls. Pages 43 ( = key), 57, Plate 5, Figure 7.
As a slightly random aside, I have a few books which belonged to Peter C Finch. This is the first slide of his that I have got though.