Place the first seven ingredients in cheesecloth and tie with butchers twine. Put the seasoning bag, water, potatoes, onions, lemons, 1 1/4 cups of the salt, 1/4 cup of the cayenne, and garlic in a large stockpot. Bring the liquid to a boil, cover and boil for 15 minutes. Add the sausage, corn, crawfish, crabs, and lobsters. Using a long handled spoon, stir around and press the contents of the pot down well into the water. Cover the pot and return to a boil. Boil for 2 minutes. Turn off the heat. Add the remaining 1 tablespoon salt and 1 tablespoon cayenne. Cover and let the boil stand for 10 minutes. Add the shrimp and clams. Return to the heat and continue to cook for 5 minutes. Drain.
Turn the shellfish boil onto newspaper. Serve with melted butter. Garnish with parsley.