A loose arrangement of Navicula hippocampus. Current name Gyrosigma attenuatum. Slide by Charles Topping, prepared for Joseph Philip Amadio (the initials ‘j.a.’ on the slide). Additionally the slide says ‘No. 20’ and ‘Test’. No paper label but the glass is etched. No date, but presumably some time around 1860. Olympus BHB microscope using 450nm LED light. 40x Leitz Pl Apo NA 1.00 objective, oil immersion. Olympus Aplanat Achromat condenser, oil immersion, oblique lighting. 2.5x Nikon CF PL photoeyepiece. Monochrome converted Nikon d850 camera. Slide was low contrast, presumably as a result of using a low refractive index mount such as Canada Balsam, so I used oblique lighting to try and emphasize the details.