They are called “Steamers” because they are usually steamed whole, but they can also be shucked then fried.
They will contain a lot of grit and sand. They need to be soaked in water with some salt and cornmeal in it to encourage them to expel this grit. Change the soaking water at least once.
1 pound (450g) Steamer Clams in shells = 10 to 14 Steamer Clams.
Depending on the locale, they are also variously known as Belly Clams, Ipswich Clams, Long-Neck Clams, Manninose Clams and Piss-Clams.