Trim a 1 inch slice from core end of lettuce head. Stand lettuce head on a flat surface. With a paring knife, cut out the center, leaving a 1/2 inch thick shell. Remove lettuce from center; reserve for another use. Wrap lettuce "bowl" in moist paper toweling and chill.
In bowl, mix shrimp, bell pepper, salsa,corn, green onions, parsley, mayonnaise, sour cream and lemon juice. Cover and chill for at least1 hour.
Put lettuce bowl on platter. Spoon dip into bowl. Arrange crudites and crackers around lettuce bowl. Makes 12 servings.