Preheat oven to 350º. Prepare cake mix according to package directions using the water and lemon juice. Stir in lime rind.
Spread in an ungreased 10' tube pan, break the air pockets by cutting through batter with a knife.
Bake on lowest oven rack for 40 min, or until cake springs back when lightly touched. Let cool, Loosen from sides of pan with a knife or metal spatula and invert onto a plate. If desired, serve with whipped topping and lime slices.