An arrangement of four Pleurosigma formosum from Mentone (I’m guessing Menton, south of France, close to the Italian border). Prepared by William Allott Firth. Olympus BHB microscope using 450nm LED light. 20x Nikon Plan Apo 0.65 objective. Olympus Aplanat Achromat condenser, oblique lighting. 2.5x Nikon CF PL photoeyepiece. Monochrome converted Nikon d850 camera. 19 images stacked in Zerene (Pmax).
Pleurosigma formosum W.Smith 1852. Published in: Smith, W. (1852). Notes on the Diatomaceae with descriptions of British species included in the genus Pleurosigma. Annals and Magazine of Natural History, Series 2 9: 1-12, 2 pls. Page 5, Plate 1, Figure 1.