Combine pecans, sugar and butter; mix well. Press on to the bottom of a 9 inch ( 23 cm ) spring form pan. Bake in 325 F oven 12 min; set aside. Beat cream cheese until smooth. Beat in brown sugar, flour and vanilla until well blended. Add eggs one at a time, mixing well after each addition. Stir in chopped turtles. Pour on to pecan crust. Bake in 325 F oven 50 ~ 60 minutes, or until centre of cake is just set. Turn off oven and let cake stand in oven 30 minutes. Remove to a wire rack, cool to room temperature. Chill for at least 4 hours before service. Garnish with whole turtles. Makes 8-10 servings.