Two examples of Euodia frauenfeldii. Both mounted with the rim upwards towards the coverslip (underside views). No location given but I have seen these on an arrangement from Australia before. Prepared by Watson and Sons Ltd. 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. 44 images stack in Zerene (Pmax).
Euodia frauenfeldii Grunow 1863. Published in: Grunow, A. (1863). Über einige neue und ungenügend bekannte Arten und Gattungen von Diatomaceen. Verhandlungen der kaiserlich-königlichen zoologisch-botanischen Gesellschaft in Wien 13: 137-162, 2 pls. Page 158, Plate 14, Figure 19. This name is currently regarded as a synonym of Eunotogramma frauenfeldii (Grunow) Grunow 1883. Published in: Van Heurck, H. (1882). Synopsis des Diatomées de Belgique. Atlas. pp. pls LXXVIII-CXXXII [78-132 and supplementary pls 22 bis, 82bis, 83bis, 83ter, 95bis], tables genres. Anvers: Ducaju et Cie. Plate 126, Figure 14. Also known by the name Moralesonia frauenfeldii (Grunow) D.M.Williams, Ts.Georgiev, T.M.Schust. & C.E.Wetzel, 2024. In: Williams, David M., Georgiev, Tsvetoslav, Schuster, Tanja M., Wetzel, Carlos E. (2024): The relationships of Eunotogramma frauenfeldii (Bacillariophyta) I. An account of its structure and description of the new genus Moralesonia. Plant Ecology and Evolution 157 (3): 270-290, DOI: 10.5091/plecevo.121829
The cribra (siliceous occlusion) within the areola have some great structure in SEM, and there is a hint of this with the image presented here.