An arrangement of six Arachnoidiscus sp. from Japan. Prepared by Samuel Henry Meakin. Mounted in Styrax and dated August 1949. They are numbered as 1 and 2 from Akita, 3 from Hakodate, and 4, 5 and 6 from Sendai. I am assuming this is from the top (top one is number 1., then 2. and 3., and finally 4., 5. and 6. on the bottom row). The lower label says ‘1. abnormal’, which I am assuming is referring to no. 1. as being an abnormal form. There is a good book on Arachnoidiscus – Brown, N.E. (1933). Arachnoidiscus. An account of the genus, comprising its history, distribution, development and growth of the frustule, structure and its examination and purpose in life, and a key to and descriptions of all known species, illustrated. pp. 1-88, 7 pls. London: W. Watson & Sons, Ltd. (available online here). In this Brown mentions A. sendaicus as being from Japan, along with something called A. hybridus, which he said contained characteristics of A. ornatus and A. sendaicus. Based on Brown’s images these look like A. sendaicus, with perhaps no. 3. being A. hybridus.
Olympus BHB microscope using 450nm LED light. 40x Leitz Pl Apo NA 1.00 objective, oil immersion. Olympus Aplanat Achromat condenser, oil immersion, oblique lighting. 2.5x Nikon CF PL photoeyepiece. Monochrome converted Nikon d850 camera. 31 images stacked in Zerene (Pmax).