Interesting slide this, with a bit to unpack. Labelled as Hydrosera tricoronata. Location given as Lake Curzon, Canterbury, New Zealand. I’ll come back to this in a minute. Single example on the slide along with four Pinnularia sp.. The main diatom is not face on, but more like tilted at 45 degrees. No makers name. 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. 49 images stacked in Zerene (Pmax). Couldn’t get close enough to use the 63x Leitz objective.
First the name. Hydrosera tricoronata Stolterfoth 1881. Published in: Stolterfoth, H. (1881). On a new species of Hydrosera Wall. Journal of the Royal Microscopical Society, series 2, 1: 424, 2 fig. Page 424, Plate V, Figures 2,3. Type Information; North Canterbury, N.Z. in sub-peat fresh-water deposit. This is a fresh water species. Quote from the page “The exact locality is not known.”. A sub-peat deposit is the layer of mineral soil, sand, clay, glacial till, or bedrock that lies directly underneath an accumulation of peat. The relevant pages from this are shown below, so the structure can be more cleared seen.
Also see Triceratium trifoliatum Cleve 1881. Published in: Cleve, P.T. (1881). On some new and little known diatoms. Kongliga Svenska-Vetenskaps Akademiens Handlingar, N.F. 18(5): 1-28, 6 pls. Page 23, Plate VI, Figure 71. This name is currently regarded as a synonym of Stoermeria trifoliata (Cleve) J.P.Kociolek, L.Escobar & S.Richardson. 1996. Published in: Kociolek, J.P., Escobar, L. & Richardson, S. (1996). Taxonomy and ultrastructure of Stoermeria, a new genus of diatoms (Bacillariophyta). Phycologia 35: 70-78, 29 figs. Page 71.
So, it looks like the current up to date name for this is Stoermeria trifoliata (Cleve).
Next the location. I cannot find reference to a ‘Lake Curzon’ in Canterbury, New Zealand. There is a Curzon Glacier, but not in Canterbury. I was initially thinking maybe a spelling mistake and it is ‘Lake Guyon’, which is in North Canterbury. From Google AI, when questioned about peat near Lake Curzon; “Yes, minor localized organic soil and shallow wetland or swamp-margin accumulation occurs near Lake Guyon, but the dominant surrounding glacial landscape is characterized by moraines and rock-basins rather than extensive peat geology.”. So there would be peat there.
However it looks like it could be Lake Sumner according to Art. XLII.—Notes on some of the Diatomaceous Deposits of New Zealand. Transactions and Proceedings of the Royal Society of New Zealand, Volume 15, 1882, Page 340-346, where it is given the alternative name Triceratium trifoliatum Cleve, n.s.. Whether this is the same place as the original example (or the one from this slide) was collected from is unclear.