A group labelled as Hemiaulus alatus by Watson and Sons Ltd (more on the name in a minute). Olympus BHB microscope using 450nm LED light. 20x Nikon Plan Apo NA 0.65 objective. Olympus Aplanat Achromat condenser, oblique lighting. 2.5x Nikon CF PL photoeyepiece. Monochrome converted Nikon d850 monochrome. 20 images stacked in Zerene (Pmax).
Hemiaulus alatus Greville, 1865. Published in: Greville, R.K. (1865). Descriptions of new and rare diatoms. Series XV. Transactions of the Microscopical Society, New Series, London 13: 24-34, 2 pl.s [III, IV]. Page 31, Plate III [3], Figure 14. Homotypic synonyms: Riedelia alata (Greville) H.J.Schrader & J.Fenner 1976, Williamriedelia alata (Greville) S.Blanco & C.E.Wetzel 2016.
However I am not convinced by this name. They look more like Hemiaulus polycistinorum to me. For example, see here.
Hemiaulus polycystinorum Ehrenberg 1854. Published in: Ehrenberg, C.G. (1854). Mikrogeologie. Einundvierzig Tafeln mit über viertausend grossentheils colorirten Figuren, Gezeichnet vom Verfasser. pp. [1]-31, 40 pls [Taf. I-XXXX]. Leipzig: Verlag von Leopold Voss. Page 15, Plate XXXVI, Figure 43a-d.