Hello, I have recently found these pycnodontes at a maastrichtian site in SE North Carolina, USA . It is Pee Dee formation. Would anyone know the speices ? The upper valve is rather flat as opposed to concave and has radiant grooves which I have not seen in my research. The lower valves vary from being almost flat on some to a deep dish concave on others. I have attached two different ones. The first picture of each is the upper valve showing the radiant grroves. Second picture is lower valve. Third picture is the hinge area. Fourth picture is an attempt to show the overall contour. Thanks