Spoon and spread the cocktail sauce into the bottom of a wide, fairly shallow 2 1/2 cup capacity bowl. Gently place the shrimp over the cocktail sauce. In a small bowl, whisk the sour cream and citrus juice together until smooth. Gently spread this mixture over the shrimp and then sprinkle with green onion. Cover and refrigerate until ready to serve. Serve with crackers or sliced baguette.