Slide labelled as Triceratium Americanum v. quad., from Oamaru New Zealand. I think this is now what is known as Stictodiscus novaezealandiae (more on this in a minute). Single example on the slide. Prepared by Frederick Marshall. Olympus BHB microscope using 450nm LED light. 63x Leitz Pl Apo NA 1.40 objective, oil immersion. Olympus Aplanat Achromat condenser, oil immersion, oblique lighting. 2.5x Nikon CF PL photoeyepiece. Monochrome converted Nikon d850 camera. 59 images stacked in Zerene (Pmax).
Back to the name. Triceratium americanum var. quadrata Grove & Sturt, 1886. Parent: Triceratium americanum (J.W. Bailey) Cleve-Euler, 1951 accepted as Tetragramma americana Bailey, 1854.
Based on appearance I think this is now what is known as Stictodiscus novaezealandiae Grunow 1888. Published in: Schmidt, A.[W.F.] (1888). Atlas der Diatomaceen-kunde. Series III: Heft 33-34 [“Heft 29-30”]. pp. pls 129-136. Aschersleben: Verlag von Ludwig Siever. Plate 131, Figure 10. Homotypic synonym: Cladogramma novaezealandiae (Grunow) Kuntze 1898. Published in: Kuntze, O. (1898). Revisio generum plantarum. Vol. 3(3) pp. 1-576. Leipzig, London, Milan, New York, Paris: Arthur Felix, Dulau & Co., U. Hoepli, Gust. E. Stechert, Charles Klincksieck. Page 401.