In large bowl combine caviar, parsley, onion and lemon rind. Stir sour cream into this mixture. In a separate bowl whip the heavy cream. Sprinkle gelatin over the water in saucepan and cook over low heat, stirring constantly until the gelatin is completely dissolved. This takes just a minute or two. Stir gelatin into the caviar and sour cream mixture. Fold in whipped cream and add pepper to taste. Line a 1-quart mold with plastic wrap and spoon mixture into mold. Chill overnight. To serve, unmold on lettuce and garnish with lemon slices. Serve with small pieces of pumpernickel bread.