In a large bowl, combine the cracker crumbs, walnuts, sugar and cinnamon. Stir in butter; set aside. In another large bowl, beat cream cheese and confectioners' sugar until smooth. Beat in ricotta cheese and lemon juice., Place 1/2 cup blueberries in each of 4 dessert dishes. Top with cream cheese mixture, crumbs and remaining blueberries. Garnish with whipped cream if desired. Refrigerate until serving.