Slide labelled as Melosira sp.? (more on this in a minute) from Barbados. Single example on the slide, mounted with the rim upwards towards the coverslip (underside view). Dated 1876. Prepared by Frederick Marshall. Interestingly the mid-late 1870s seems to be quite a late date for him. Olympus BHB microscope using 450nm LED light. 63x Leitz Pl Apo NA 1.4 objective, oil immersion. Olympus Aplanat Achromat condenser, oil immersion, oblique lighting. 2.5x Nikon CF PL photoeyepiece. Monochrome converted Nikon d850 camera. 42 images stacked in Zerene (Pmax). I also did a partial stack without the rim, to show the tubes coming out of the side of the body of the diatom.
Back to the name. I am 99.9% sure this is not a Melosira. The general shape and look of the rim and the tubes coming from the main part of the body reminded of Porodiscus hirsutus. But the central part looks very different. Long story and lots of looking through articles and books, but another option was Pseudopodosira, and chatting with a couple of experts has pushed this towards being a Pseudopodosira sp. of some type. I’ll add more information as and when it comes up. An interesting looking diatom and different to anything I have seen before.
EDIT – after a few conversations I’ve been told that this has similarities with (but is not 100% match with) Pseudopodosira jouseana Sar, Lavigne, Wetzel, Ector & Sunesen 2017. Published in: Sar, E.A., Lavigne, A.S., Wetzel, C.E., Ector, L. & Sunesen, I. (2017). Pseudopodosira boltovskoyi sp. nov. (Pseudopodosiraceae, Bacillariophyta) from coastal waters of Argentina. Phycologia 56(3): 239-252, 56 fig., 1 table. Page 250.