Slide simply labelled ‘?’, from S. Monica (presumably Santa Monica). Single example, shown partially oblique. I’ll come back to my thoughts on the name in a minute. Olympus BHB microscope using 450nm LED light. 63x Leitz Pl Apo 1.4 objective, oil immersion. Olympus Aplanat Achromat condenser, oil immersion, oblique lighting. 2.5x Nikon CF PL photoeyepiece. Monochrome converted Nikon d850 camera. 57 images stacked in Zerene (Pmax). Some nice dotting more easily seen in some of the unstacked frames when the contrast is boosted a bit more.
I’ve settled on the name Entopyla australis (maybe the var. miniscula or maybe something in between the two) for this. Here’s how. The first place I looked was Schultze, E. A., and C. Henry Kain. “The Santa Monica Diatomaceous Deposit with List of References to Figures of Species.” Bulletin of the Torrey Botanical Club, vol. 24, no. 11, 1897, pp. 496–504. JSTOR, https://doi.org/10.2307/2478070. This is a nice reference which gives a good list of the species from Santa Monica. Looking through this and Schmidt’s Atlas, I thought it looked like an Entopyla of some type, perhaps a small version of Entopyla australis. Gephyria gigantea appears in Schultze and Kain’s article, and Gephyria gigantea f. gigantea is another name for E. australis var. gigantea. However this one looked a little small to be E. australis. Digging further I came across Frenguelli, J. (1930). Contribuciones al conocimiento de las diatomeas Argentinas. VI. Diatomeas marinas de la costa Atlántica de Miramar (Prov. de Buenos Aires). Anales del Museo Nacional de Historia Natural, 35: 243-312, 10 pls. Specifically on page 289; pl. IV, fig. 8 it describes Entopyla australis var. miniscula. Image shown above, and translation below;
“Entopyla australis var. minuscula n. var. (Plate IV, fig. 8)
I have grouped the smallest individuals under this name. Their extremely small dimensions, especially when compared to those of individuals of the previous variety, are also accompanied by a greater density of transverse ribs. Valve: length 0.039-0.045 (mm); width 0.019-0.020 (mm); ribs 3 1/2-4 in 0.01 (mm).”
The one on the slide is bigger than this – 0.076mm long – and fits in between E. australis and E. australis var. miniscula in terms of length. E. australis is shown in the reference on Plate IV, Figs 1,2 and also above. Hence I think this could be E. australis or E. australis var. miniscula (or something in between), however I shall leave it with a question mark for now.
I recently acquired about 60 slides by this maker, so if you want to see others by them, search for AAAAA in the Search option at the top of the page, and I’ll include this in each of the pages for them.