Slide labeled as Arachnoidiscus ornatus var. montereyi prepared by WH Darlaston. There is something which looks like ‘Constantinople’ on the top label, which may be the location. Olympus BHB microscope using 450nm LED light. As well as the arrangement, I imaged the smaller one using a 40x Leitz Pl Apo 1.00 objective, oil immersion. Olympus Aplanat Achromat condenser, oil immersion, oblique lighting. 2.5x Nikon CF PL photoeyepiece. Monochrome converted Nikon d850 camera. 37 images stacked in Zerene (Pmax). This is rim upwards towards the coverslip, i.e. an underside view.
Could find an exact match for the name but this could be Arachnoidiscus ornatus var. montereianus A.W.F.Schmidt 1882. Published in: Schmidt, A.[W.F.] (1882). Atlas der Diatomaceen-kunde Series II : Heft 19. pp. pls 73-76. Aschersleben: Ernst Schlegel’s Verlag. Plate 73, Figures 7-9 (as ‘montereiana‘).