Slide labelled as Aulacodiscus from Moreno Shale, California. I’ll come back to my thoughts on the name in a minute. Dated Jan [19]46, and mounted in Styrax. There’s no makers name, but based on the style, and some others I have seen for sale I think this is by WF Reeve (I am currently not sure if this is the same WF Reeve as some other slides I have by Wallace Frederick Reeve such as here as the style is different). Olympus BHB microscope using 450nm LED light. For the single diatom – the larger one of the two – 63x Leitz Pl Apo 1.40 objective, oil immersion. Olympus Aplanat Achromat condenser, oil immersion, oblique lighting. 2.5x Nikon CF PL photoeyepiece. Monochrome converted Nikon d850 camera. 50 images stacked in Zerene (Pmax). Also a Trinacria sp. present.
Ok, the name. I think these two are Aulacodiscus pugnalus. My reasoning. A diatom called A. simbirskianus var. pugnalis is described in: John A. Long, Dingley P. Fuge, James Smith, Diatoms of the Moreno Shale, Journal of Paleontology, Vol. 20, No. 2 (Mar., 1946), pp. 89-118. Page 97, Plate 13, Figure 12. This is a good match both visually and the description. This article refers to an earlier document in which it is called Aulacodiscus pugnalis. The paper referred to is Hanna, G.D. (1927). Cretaceous diatoms from California. Occasional Papers of the California Academy of Sciences 13: 5-[49]. Pages 14,15, Plate 1, Figures 6,7. In this it is spelt ‘pungalus‘ a couple of times as well as ‘pugnalis‘. In the WoRMS database it states that the accepted name is A. pugnalus (see here). This is why I am going with the name A. pugnalus, although keep in mind the others when looking for examples if it.