A slide of Pleurosigma parkeri from Crocodile Creek, USA in an arrangement with a second diatom. More on the name later. There look to be two P. parkeri, one on top of the other. Prepared by JA Long and mounted in Hyrax. Olympus BHB microscope using 450nm LED light. 63x Leitz Pl Apo 1.4 objective, oil immersion. Olympus Aplanat Achromat condenser, oil immersion, brightfield lighting. 2.5x Nikon CF PL photoeyepiece. Monochrome converted Nikon d850 camera. 9 images stacked in Zerene (Pmax) and I just picked the photos for the top P. parkeri as stacking everything muddied the final result.
Back to the name. P. parkeri (also seen as P. parkerii) is described in Harrison, M. (1860). On a new Pleurosigma. Quarterly Journal of Microscopical Science, new series 8: 104-105. This name is currently regarded as a synonym of Gyrosigma wormleyi (Sullivant) Boyer, published in: Boyer, C.S. (1922). New and rare species of Diatomaceae. Contributions from the Biological and Microscopical Section of the Academy of Natural Sciences of Philadelphia 1: 1-17.