Boil the lobster. Drain and cool. Remove meat from shell, reserving liver, and cut meat in small pieces. Cover bodies with cold water, and simmer 15 minutes. Strain, add the potatoes to stock, and cook until tender. In saucepan, melt butter and cook onion until delicately browned. Blend in lobster liver, then stir in flour. Pour milk in gradually, stirring until thickened. Add lobster meat, potatoes, stock, and seasoning. Simmer 5 minutes. Split common crackers. Place in hot tureen and pour chowder over crackers. Sprinkle with parsley.