Observaciones de jfraser

I would appreciate any help in identifying these large, heavy, well worn mussels. They are all single halves with three photos for each. I believe they are likely all the same species. They are quite inflated and the shell is significantly thicker at the anterior end. The only mussels I have found at this site that are this large is Fluttedshell. Too large for Fatmucket. Could they be Muckets? Your thoughts/input is appreciated.