This one was fun to identify. Asteromphalus nancoorensis var. minor (slide labelled as Asteromphalus new species, but I was able to put a name to it) from Conset, Barbados. Single example on the slide. No makers name and there is something which says ’52 (maybe dating it to 1952?). 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. 65 images stacked in Zerene (Pmax).
So, the name. Asteromphalus nancoorensis var. minor Grunow is mentioned in an article by J.H. Robinson which lists the species found at Conset – JH Robinson, The occurrence and distribution of the diatoms in the oceanic beds of Barbados (Conset). The Journal of the Barbados Museum and Historical Society. May 1936, 3(3), 149-152. Copy from The Barbados Museum and Historical Society (https://www.barbmuse.org.bb/). This article does not give an image though, just a name.
This species is illustrated in HF van Heurck, Synopsis des Diatomées de Belgique, Atlas et Table, Plate 127 (CXXVII), Figure 13, and does match what I have here. That one was from the deposit at Naparima, Trinidad.
An interesting looking Asteromphalus, especially with the three spikes at the top of the central region.