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Hi, @Patrick-Hsieh, either the Dry Dredgers link I sent or the https://www.ordovicianatlas.org/ would be useful here too for IDs.

@samantha-ocon Its difficult to tell the difference between Rafinesquina and Strophomena in the Dry Dredgers pictures. The Ordovician Atlas lists internal characteristics that are not visible in this specimen. The interior of the valve is cemented with a hard matrix and my air scribe and air blaster can’t really break through without damaging the specimen itself. My old copy of Index Fossils of North America by Shimer and Shrock indicates Rafinesquina valves are concavo-convex or plano-convex while Strophomena are convexo-concave. I don’t see evidence of a pedicle foramen, deltidium or muscle scars. Could this be a brachial valve? In which case it is convex and would point to Strophomena.

Hi @Patrick-Hsieh, I definitely think this is a brachial valve. I believe your identification of Strophomena makes sense, and I will mark this research grade.