A strew of Gomphonema geminatum (and a few other different diatoms). No makers name or location. Olympus BHB microscope using 450nm LED light. As well as the strew, I did stacks of Gomphonema geminatum and Tetracyclus emarginatus using the 63x Leitz Pl Apo 1.4 objective, oil immersion. Olympus Aplanat Achromat condenser, oil immersion, oblique lighting. 2.5x Nikon CF PL photoeyepiece. Monochrome converted Nikon d850 camera. Images stacked in Zerene (Pmax). The Tetracyclus is view from the underside with the rim towards the coverslip, and shows two rimoportulae in the middle section.
Gomphonema geminatum (Lyngbye) C.Agardh, 1824. Published in: Agardh, C.A. (1824). Systema algarum. pp. [i]-xxxvii, [1]-312. Lundae [Lund]: Literis Berlingianis [Berling]. Page 12. This name is currently regarded as a synonym of Didymosphenia geminata Mart.Schmidt, 1899. Published in: Schmidt, A.[W.F.] (1899). Atlas der Diatomaceen-kunde. Series V: Heft 54 . pp. pls 213-216 [M. Schmidt]. Leipzig: O.R. Reisland. Plate 214, Figures 7-10.
Tetracyclus emarginatus (Ehrenberg) W.Smith 1856. Published in: Smith, W. (1856). A synopsis of the British Diatomaceae; with remarks on their structure, functions and distribution; and instructions for collecting and preserving specimens. The plates by Tuffen West. In two volumes. Vol. II. pp. [i]-xxix, 1-107, pls 32-60, 61-62, A-E. London: John van Voorst, Paternoster Row. Page 38.