For N=2 SUSY theories with non-vanishing β-function and one-dimensional quantum moduli, we study the representation on the special coordinates of the group of motions on the quantum moduli defined by Γ_W=Sl(2;Z)/Γ_M, with Γ_M the quantum monodromy group. Γ_W contains both the global symmetries and the strong-weak coupling duality. The action of Γ_W on the special coordinates is not part of the symplectic group Sl(2;Z). After coupling to gravity, namely in the context of non-rigid special

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... y, we can define the action of Γ_W as part of Sp(4;Z). To do this requires singular gauge transformations on the "scalar" component of the graviphoton field. In terms of these singular gauge transformations the topological obstruction to strong-weak duality can be interpreted as a σ-model anomaly, indicating the possible dynamical role of the dilaton field in S-duality.