Surirella gemma, unknown mounter

Surirella gemma
Surirella gemma and pleurosigma angulatum

Strew slide with Surirella gemma and other species such as Pleurosigma angulatum. No mounters name. There is some engraving on the glass and I think the final part of the date is 91 (presumably 1891). The mountant is piperine. Olympus BHB microscope using 450nm LED light. 60x Olympus Splan Apo NA 1.4 objective, oil immersion. Olympus Aplanat Achromat condenser, oil immersion, oblique lighting. Olympus 3.3x and 2.5x NFK photoeyepieces. Monochrome converted Nikon d800 camera. Images stacked in Zerene (Dmap). Piperine as a mountant is mentioned in “the study of diatoms” by Samuel Meakin, pages 209-212, an article in Microscope & Entomological Monthly, 1939, Vol III, No. I. It is a described as an easy mountant to work with, although relatively few slides with it seem to exist now.