?Cyrtodontula compressa

Whitella is an invalid genus name - all specimens once called Whitella is in Cyrtodontula. Found in Decorah shale - the largest uncommon bivalve I have ever found in Decorah Shale as of 2021. There could be others since all bivalves are listed as uncommon to rare in Decorah shale. It could be my bias but oddly enough I only find mold impressions of this one (all 3 individuals) as negative molds in limestone without any hard shale encrust in the hollows. Trying Paint to show outlines - strongly resembles modern Anadara notabilis in general shape for example - its NOT related to Anadara. I'm only picking the name Cyrtodontula compressa for now since its the only one that at least for me closely resembles the fossils in shape and sizes. Forgot to add ruler so measurements roughly from where estimated hinge line to farther part of the mold is 50 mm for the two smaller individuals and 60 mm for the larger individuals.