A strew slide labelled as Nitzschia curvula (various species and genus present). Mounted dry. No makers name, but prepared by Ernest Hinton. Olympus BHB microscope using 450nm LED light. As well as the strew I selected one to image 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. 14 images stacked in Zerene. Very difficult to make out the striae.
I also imaged one using 365nm oblique light (Lomo ОИ-14 condenser, oblique, water immersion), and on that one I could see the striae a bit clearer. Striae spacing about 290nm (34.5 striae per 10µm).
As for what the ones I image are, that is a good question. Having looked up Nitzschia curvula, one description seems to be an illegal name, the other is now described as an Iconella. Neither of these seem like good options. To me it looks like Nitzschia sigma, but the striae spacing is very small. However I did find a mention of 40 striae per 10µm for it in: Contribution to the current list of Nitzschia species (Bacillariophyceae) in Malaysia, Acta Aquatica: Aquatic Sciences Journal, 8:2 (August, 2021): 78-86. DOI: https://doi.org/10.29103/aa.v8i2.4777. Page 81, Figure 8. So, maybe N. sigma?