An arrangement labelled as Cocconeis regina from Maccabe Island (I am assuming Macabi Island off the coast of Peru where extensive guano harvesting was done). Label on the back says “7 frust[ules] rather dim and v. [can’t read that word]”. Prepared by Laurence Hardman. Olympus BHB microscope using 450nm LED light. As well as the arrangement I imaged one with 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. 23 images stacked in Zerene (Pmax).
Cocconeis regina C.Johnston. See: Johnston, C. (1860). Descriptions of Diatomaceae, chiefly of those found in “Elide” (Lower California) Guano. Quarterly Journal of Microscopical Science 8(2): 11-21, pl. 1. Page 13, Plate 1, Figure 12.
A very interesting look diatom, and I’m not 100% convinced by the Cocconeis name. Features of interest – the small dots on the large features at either end of the central axis, and there are small holes (rimoportulae) all about the same distance inside the rim and all the way around it.
EDIT – after a chat with David Walker at the Natural History Museum, I now have a name for this. Indeed it is not a Cocconeis, but in fact a Diplomenora sp., presumably Diplomenora cocconeiformis (as this is a monotypic diatom). Publication Details: Diplomenora cocconeiformis (A.W.F.Schmidt) K.L.Blazé 1984. Published in: Blazé, K.L. (1984). Morphology and taxonomy of Diplomenora gen. nov. (Bacillariophyta). British Phycological Journal 19: 217-225, 13 figs, 1 table. Page 218, Figures 1–12 (as ‘cocconeiforma‘). I should note that mine is both larger (62µm long axis, 58µm short axis) and with more rimoportulae (14 compared with 4-9) from the description in Blazé’s 1984 paper. However other than it is a good match, so perhaps the one I chose to image is quite a large one. From what I can tell a rather unusual and interesting diatom with not much known about it.