Triceratium lineatum f. biangulata from Papakaio, Oamaru, New Zealand. Single example on the slide. Mounted in Styrax, and dated 12/6/[19]41. Some debris and crystals over the diatom. No makers name, but I think this is by WF Reeve (but will leave it with a question mark for now). 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. 41 images stacked in Zerene (Pmax). Got a bit lucky with this one. By the bottom of the stack the objective was touching the slide (probably the coverslip ring).
Triceratium lineatum f. biangulata Laporte & Lefebure, 1930. Original description: Laporte, L.J. & Lefébure, P. (1930). Diatomées rares et curieuses, Vol. 2. Paris, pls 16-30. Plate 26, Figure 185. Also see Trigonium lineatum f. biangulata (Laporte & Lefebure) Desikachary & Sreelatha, 1989. I think this is also known as Trigonium lineatum var. lineatum f. biangulata.