Trigonium taeniatum (slide labelled as Triceratium lineatum, but I think this is more likely Trigonium / Triceratium taeniatum) from Oamaru, New Zealand. Single example on the slide. Prepared by Thomas Edward Doeg. 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. 11mm removed from the tube the camera to increase the field of view. Monochrome converted Nikon d850 camera. 121 images stacked in Zerene.
Triceratium lineatum Greville, 1863. Published in: Greville, R.K. (1863). Descriptions of new and rare Diatoms. Series IX. Transactions of the Microscopical Society, New Series, London 11: 63-76, pls IV, V. Page 75, Plate V [5], Figure 24. This name is currently regarded as a synonym of Trigonium lineatum (Greville) Desikachary & Sreelatha, 1989. Published in: Desikachary, T.V. & Sreelatha, P.M. (1989). Oamaru diatoms. Bibliotheca Diatomologica 19: [1]-330, including 145 plates. Page 278, Plate 124, Figure 2.
Triceratium taeniatum Hustedt, 1959. Published in: Schmidt, A.[W.F.] (1959). Atlas der Diatomaceen-kunde. Series VIII (Heft 117-118) [F. Hustedt]. pp. pls 465-472. Akademie-Verlag. Plate 471, Figure 1 (as ‘Triceratium (Trigonium) (lineatum var.?) taeniatum‘). Also see: Desikachary, T.V. & Sreelatha, P.M. (1989). Oamaru diatoms. Bibliotheca Diatomologica 19: [1]-330, including 145 plates. Page 281, Plate 124 Figures 3,9,12, Plate 136 Figure 1.
This more closely matches the description/images for T. taeniatum.