I originally thought I was going to have to describe this as ‘unknown diatom, unknown maker’, but after a bit of searching I am fairly sure this is Campylodiscus pfitzeri from Tamatave (Toamasina, Madagascar). Single example on the slide. I’ll explain more about the name in a minute. No makers name. Olympus BHB microscope using 450nm LED light. 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. 100 images stacked in Zerene (Pmax).
Right, the name. The slide came unlabelled, and all I had was the location – Tamatave. Initially I thought this might be a Surirella of some type, however I couldn’t find anything which matched it. After thinking about it I settled on it potentially being a Campylodiscus. In the book by Deby, J. (1891, Analysis of the Diatomaceous Genus Campylodiscus. Privately published, London) I was looking through the plates and came across something described as Campylodiscus horologium and C. horologium var. pfitzeri on Plate VI, Figures 29a and b. These looked very similar to mine, with Fig 29b, C. horologium var. pfitzeri being the closest match. This also appears in Schmidt’s Atlas under the name Campylodiscus pfitzeri on Plate 17, Figs 5,6, and I understand C. pfitzeri is the currently accepted name. Hence I am going with Campylodiscus pfitzeri for this one. Still no idea as to the maker though.