Triceratium, new species (more on the new species part in a minute) from Mejillones, Chile. Fossil guano. Single example on the slide, shown as a side view. Prepared by Arthur Charles Cole. Olympus BHB microscope using 450nm LED light. 63x Leitz Pl Apo NA 1.4 objective, oil immersion. Olympus Aplanat Achromat condenser, oblique lighting.2.5x Nikon CF PL photoeyepiece. Monochrome converted Nikon d850 camera. 71 images stacked in Zerene (Pmax).
For ID’ing this, I initially looked at Joaquin Frenguelli, Diatomeas fósiles de los yacimientos chilenos de Tiltil y Mejillones, Darwiniana T. 9, No. 1 (diciembre 1949), pp. 97-157. This gives listed a few Triceratium species. Looking through the descriptions and references, I have settled on this one most likely being Triceratium mammiferum Grun. or Triceratium mammiferum f. minor. There was no image of these in the paper above, but they are shown in Van Heurck, H. (1880). Synopsis des Diatomées de Belgique. Atlas. Ducaju & Cie., Anvers. Plate 112, Figure 6 (T. mammiferum) and Plate 112, Figure 7 (T. mammiferum f. minor). The f. minor in particular is a very good visual match for this one.
This is how T. mammiferum was described in the Frenguelli paper (on page 124): “A rare fossil species, found by Möller in a piece of tripoli [porous, siliceous rock] of unknown origin, found floating in the Elbe River, Germany (ref 45, plate 112, figs. 6-7); Tempère and Peragallo (ref 43, p. 16) list it as rare in the marine Eocene deposit of Jutland, Denmark. Möller reports it in Mejillones.”. I learnt something today, that ‘tripoli’ is a porous, silica rock.