A strew from Point Dume, California, USA. Fossil marine material (late Miocene, part of the Monterey formation). Diatomite sample from H Jay Margolis. Diatom sample from the collection of Colonel William D Fleming, US Army, MD FRMS. Mounted in Pleurax and dated 31/5/2026. Prepared by Michel Haak. Olympus BHB microscope using 450nm LED light. As well as the wider view I imaged an example of what I think is Auliscus mirabilis using the 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. 43 images Pmax. Underside view with the rim upwards towards the coverslip.
Auliscus mirabilis Greville, 1863. Original description: Greville, R.K. (1863). A monograph of the genus Auliscus. Transactions of the Microscopical Society, New Series, London, 11(3): 36-53, pls II & III. Page 47, Plate 2, Figure 11.
From Greville, 1863: “Habitat, Monterey stone. An exquisitely beautiful diatom, and rare as beautiful.”. It certainly is a striking diatom. For other examples of it, viewed from the top rather than the underside, see here and here. Same species, very different photos.