A strew slide of Nitzschia sigma and a few others. Test slide with a coverslip thickness 0.16-0.20mm. Coverslip cracked, some crystallization of the mountant, and some mold visible. Prepared by Johann Diedrich Möller. Olympus BHB microscope using 450nm LED light. As well as the wider field of view of the strew, I imaged one 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. 30 images stacked in Zerene (Pmax). Approx 507nm striae spacing (19.7 striae per 10µm) measured in Image J. The diatoms have the appearance of having been sintered onto the coverslip, especially visible in the 63x image before cleaning up, although this is not specified on the slide.
Nitzschia sigma (Kützing) W.Smith 1853. Published in: Smith, W. (1853). A synopsis of the British Diatomaceae; with remarks on their structure, function and distribution; and instructions for collecting and preserving specimens. The plates by Tuffen West. In two volumes. Vol. I. pp. [i]-xxxiii, 1-89, pls I-XXXI. London: John van Voorst, Paternoster Row. Page 39, Plate XIII [13], Figure 108.