I’m going out on a bit of limb with this one with regards to the naming. The slide is labelled Auliscus peruvianus from Vera Crux. I will come back to this in a minute. Prepared by Laurence Hardman. Olympus BHB microscope using 450nm LED light. Full arrangement using a 20x Nikon Plan Apo NA 0.65 objective. The two from the upper right of the arrangement were also imaged using a 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. 51 images stacked in Zerene (Pmax) for the two.
Ok, back to the name. Auliscus peruvianus (F.Kitton ex Ralfs) Greville 1862: 25. Basionym: Eupodiscus peruvianus Kitton ex Ralfs. This name is currently regarded as a synonym of Pseudauliscus peruvianus (Kitton ex Ralfs) A.W.F.Schmidt 1875. Published in: Schmidt, A.[W.F.] (1875). Atlas der Diatomaceen-kunde. Series I: Heft 8. pp. pls 29-32. Aschersleben: Verlag von Ernst Schlegel. Plate 32, Figure 29.
However I am pretty sure these are not Auliscus (or Pseudauliscus). I think these (the ones around the outside at least) are Ralfsiella smithii. The middle one, maybe Pleurosira laevis?
Ralfsiella smithii (Ralfs) P.A.Sims, D.M.Williams & Ashworth 2018. Published in: Sims, P.A., Williams, D.M. & Ashworth, M.[P.] (2018). Examination of type specimens for the genera Odontella and Zygoceros (Bacillariophyceae) with evidence for the new family Odontellaceae and a description of three new genera. Phytotaxa 382(1): 1-56, 156 figs, 2 text-figs. Page 42, Figures 148-151. Basionym: Cerataulus smithii Ralfs 1861. Published in: Pritchard, A. (1861). A history of infusoria, including the Desmidiaceae and Diatomaceae, British and foreign. Fourth edition enlarged and revised by J. T. Arlidge, M.B., B.A. Lond.; W. Archer, Esq.; J. Ralfs, M.R.C.S.L.; W. C. Williamson, Esq., F.R.S., and the author. pp. [1]-xii, [1]-968, 40 pls [I-XV]. London: Whittaker and Co.. Page 847.
See: Solorzano, G. G., González Fernández, J. M., & Fuentes Zuno, S. A. (2024). Phytoplankton from a brackish lagoon in the central region of Veracruz, Mexico. Revista De Biología Tropical, 72(1), e51160. https://doi.org/10.15517/rev.biol.trop.v72i1.51160. Figure 3a (Cerataulus smithii).
This is a bit of a weird one, and I’m not really sure as to how these could be thought to be Auliscus.