Actinoptychus wittii from Oamaru, New Zealand. Single example on the slide. No makers name, but prepared by Laurence Hardman. 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. 88 images stacked in Zerene (Pmax).
Actinoptychus wittii Janisch 1886. Published in: Schmidt, A., Schmitz, M., Fricke, F., Müller, O., Heiden, H. & Hustedt, F. (1874-1959). Atlas der Diatomaceen-Kunde. 4 Bands, pls. 1-480. Leipzig. Plate 100, Figure 12. This name is currently regarded as a synonym of Actinoptychus wittianus Truan & Witt 1888. Published in: Truan y Luard, A. & Witt, O.N. (1888). Die Diatomaceen der Polycystinenkreide von Jérémie in Hayti Westindien. pp. [1]–38, incl. 7 pls [I-VII]. Berlin: Verlag von R. Friedländer & Sohn. Page 10, Plate 2, Figures 18-19.
To me this one looks more like A. decorans according to Päule Heck’s Oamaru diatoms book. Also see (https://diatomimaging.com/actinoptychus-decorans-t-peters/) for the discussion of A. decorans and A. wittianus.