Strew slide from Conkey Pond, Nova Scotia, Canada. Variety of species. Mounted in Naphrax and dated June 1975. Prepared by Bernard Hartley. Olympus BHB microscope using 450nm LED light. I chose an example of an Stauroneis sp. for high magnification imaging. 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. 46 images stacked in Zerene (Pmax). Coverslip ring prevented me from using the 63x Leitz objective.
I think this is probably Stauroneis phoenicenteron.
Seems to be slide 695B Bernard Hartley’s Sample and Strew Slide Collection PDF (accessed from here). However this slide does not have an ID number so I can’t be certain.