There is a local species, called the blood ark. They commonly wash ashore because they are fouled by codium algae mops. Look it up for a reference picture on google. Beaches on the south side of the cape, on Nantucket Sound and in Buzzards Bay (from New Bedford to the canal and the whole cape side of the bay have many of these, as well as the eastern side of Cape Cod Bay. They have a beard like layer of fur on the shell. Recently, some Massachusetts shell fishermen began harvesting them, mostly the bull raking quahog diggers. They are also found in Rhode Island and further south. Good collection beaches include Little Harbor beach in Wareham, Onset Beach, the Harwich Beaches, West Dennis Beach, South Yarmouth Beaches, the Brewster Flats, Wellfleet Harbor if you want to give that a try. I have seen a bullraker land two whole onion sacks full from Wellfleet Harbor in one morning’s work. Recently. Make sure you check local regulations. Shellfish wardens give fines. Call the town warden you plan to visit first, all town websites list a number for these guys. They will answer you.