An arrangement of 5 diatoms from Santa Monica. I’ll come back to the slide name (and their names) in a minute. 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. 62 images stacked in Zerene (Pmax). I got lucky with this one, just managing to image all 5 at the same time with the 40x objective. I added a small border around the visual image so it doesn’t look too crowded.
Ok, slide name and diatoms names. The slide says “Triceratium parallelum, Harrisonianum and 2 others”. This to me implies 4 different diatoms, i.e. 2 are the same. In the image, 1, 2 and 4 are definitely different to each other, so are 3 and 5 meant to be the same? Confusing. For names, I looked at three references;
Schmidt’s Atlas (obviously).
Van Heurck, H. (1880). Synopsis des Diatomées de Belgique. Atlas. Ducaju & Cie., Anvers.
Schultze, E. A., & Kain, C. H. (1897). The Santa Monica Diatomaceous Deposit with List of References to Figures of Species. Bulletin of the Torrey Botanical Club, 24(11), 496–504. https://doi.org/10.2307/2478070
Using Schultze I went through and listed all the Triceratia, then looked at images for these and compared them with the ones from the slide. Here is where I have come out based on appearances and Schultze’s list of what is present at Santa Monica;
1. Underside view with the rim upwards. Schmidt’s Atlas Plate 79, Figure 3, Triceratium formosum (tetragona variant). Possibly.
2. Schmidt’s Atlas Plate 81, Figure 4, Triceratium arcticum var. californica forma tetragona. Fairly likely.
3. Schmidt’s Atlas Plate 75, Figure 13, Triceratium parallelum forma trigona. Fairly likely.
4. Schmidt’s Atlas Plate 468, Figure 5, Triceratium (Trigonium) obtusangulum. Plate 76, Figure 20, Triceratium punctatum. Not sure about these two, they have some similarities to the image though so am mentioning them. Van Heurck Plate 110, Figure 4, Triceratium inelegans var.(?) yucatensis. This looks to be a good match, and T. inelegans was reported in Santa Monica by Schultze.
5. Schmidt’s Atlas Plate 452, Figure 11 Stictodiscus grunowii f. trigona. Plate 448, Figure 5 Stictodiscus pulchellus. Again, not sure with these two, but they have some similarities so am mentioning. Schmidt’s Atlas Plate 76, Figure 14, Triceratium parallelum forma trigona. Looks likely a pretty good match.
From the above, you’ll notice no T. harrisoninaum. Looking at images of it in Schmidt, these just don’t look right for it. I have an example of it on this site (here). While the overall shape looks like 5. in this image, in most of the images of T. harrisonianum I have seen it has the ‘flowing lines’ in the central region, which the one on this slide does not. Also, Schultze does not mention T. harrisonianum for Santa Monica. So I am left with a few puzzlers. Nice diatoms, but names uncertain for now.