Fusion excitation functions for the reactions of Sn-¹²⁴,Sn-¹³² with Ca-⁴⁰,Ca-⁴⁸ were measured at energies near and below the Coulomb barrier. Weak sub-barrier fusion enhancement accounted for by coupling to the first 2(+) and 3(-) states in the target and projectile was observed for Sn-¹²⁴,Sn-¹³² + Ca-⁴⁸. However, the Sn-¹²⁴,Sn-¹³² +...