Omphalopelta versicolor, entire frustule. Single example on the slide. Described as very rare and is a fossil. Prepared by Arthur Charles Cole. A second set of more recent labels on the rear of the slide. Bowed slide, severe crazing in the mountant, some bubbles/lenses in the mountant around the diatom. I was lucky with this one that the area close the diatom is not that bad. 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. 61 images stacked in Zerene (Pmax).
Original description: Ehrenberg, C.G. (1844). Untersuchungen über die kleinsten Lebensformen im Quellenlande des Euphrats und Araxes, so wie über eine an neuen Formen sehr reiche, marine Tripelbildung von den Bermuda-Inseln. Bericht über die zur Bekanntmachung geeigneten Verhandlungen der Königlich-Preussischen Akademie der Wissenschaften zu Berlin, 1844: 253-275, 1 pl. Page 270. I presume this is the same as Actinoptychus heliopelta var. versicolor.