A nice arrangement of six Stictodiscus diatoms from the Galapagos Islands. No makers name but I understand this was by HRS Williams. Olympus BHB microscope using 450nm LED light. 63x Leitz Pl Apo 1.4 objective, oil immersion for most of the individual images (apart from one which was with a 40x Leitz Pl Apo NA 1.00 oil immersion objective). Olympus Aplanat Achromat condenser, oil immersion, oblique lighting. 2.5x Nikon CF PL photoeyepiece. Monochrome converted Nikon d850 camera. Image stacks prepared in Zerene (Pmax).
Next, names. I’m not too good on these Stictodiscus ones, so there will be a lot of question marks (apart from one which I am very confident about). Going from left to right in the arrangement.
Stictodiscus sp. Large, almost round one (40x Leitz objective). Underside view. 51 images stacked. Maybe Triceratium disciforme (Stictodiscus disciforme, from Barbados, Schmidt’s Atlas Plate 75, Figure 9), Stictodiscus harrisonianus (Schmidt’s Atlas Plate 448, Figures 6-11, pretty good visual match).
Stictodiscus margaritiferus (Schmidt’s Atlas Plate 451, Figure 4, Challenger Expedition S115). This name is currently regarded as a synonym of Amphitetras margaritifera (Cleve) De Toni. Published in: Castracane, [C.A.] F. (1886). Report on the Diatomaceae collected by H.M.S. Challenger during the years 1873-76. In: Report on the Scientific Results of the Voyage of H.M.S. Challenger during the years 1873-76. Botany. Vol. II. (Murray, J. Eds), pp. [1]-178. p. 115. On Page 115 referred to as a ‘coronated Stictodiscus’. Two images – top part (58 images stacked) and bottom part (14 images stacked). Also described (as T. margaritiferum) in Cleve, P.T. (1881). On some new and little known diatoms. Kongliga Svenska-Vetenskaps Akademiens Handlingar, 18(5): 1-28, 6 pls. Page 26, Plate VI, Fig 76 (shown below).
Stictodiscus sp. Small. 41 images stacked. Maybe Stictodiscus buryanus or perhaps Stictodiscus johnsonianus based on the single lines of dots near the rim.
Stictodiscus sp. 38 images stacked. Slightly larger diameter than the previous one. Maybe Stictodiscus buryanus or perhaps Stictodiscus johnsonianus again.
Stictodiscus trigonus. This one is above the previous round one, and presumably has moved from it’s original location in the arrangement. Fairly sure on this ID based on a couple of USGS Deep sea drilling docs, 29 and 12, although am leaving it with a question mark for now. 46 images stacked. Underside view. Heavily tilted downwards towards bottom right.
Finally, a shield shaped Stictodiscus. Underside view, 31 images stacked. Various possibilities; Stictodiscus parallelus (Triceratium parallelum forma trigona), Stictodiscus parallelus var. gibbosa? Stictodiscus gibbosus (Schmidt’s Atlas Plate 447, Figures 12-15), Stictodiscus harrisonianus (Schmidt’s Atlas Plate 448, Figures 6-11 are a pretty good match, especially 9 and 10). Basically not sure.