Place steamers in a large bowl. Add enough water to cover. Add cornmeal, and stir to thoroughly combined. Let stand for at least 3 hours and up to 6 hours to allow the clams to purge their sand.
Remove clams from water, and rinse thoroughly. Refrigerate until ready to use.
In a large saucepan, combine beer and 2 cups water. Bring to a boil over medium-high heat. Add clams, and cook, covered, until the clams have opened, 3 to 4 minutes. Remove clams with a slotted spoon, discarding any clams that have not opened or ones with broken shells, to a large bowl. Sprinkle with parsley.
Strain cooking liquid through a cheesecloth-lined sieve. Serve clams immediately with lemon wedges, hot broth, and melted butter.