Dissolve jello powder in boiling water. Set aside to cool.
In a bowl, combine wafer crumbs & sugar; add margarine & mix well. Reserve 1/2 cup for topping. Press remainder into an 8-inch spring form pan.
Combine cream cheese, sugar & lemon extract in a mixer bowl; beat until combined. Stir in lemon jello mixture then fold in thawed whipped topping until well blended.
Pour over crust; sprinkle with reserved crumbs & refrigerate at least 4 hours or overnight.