  We construct a $\bar Q_l$-linear Tannakian category attached to a smooth
projective curve C equivalent to the category of finite dimensional $\bar
Q_l$-representations Rep(G), where G is $Sp(2g-2,\bar Q_l)$ or $Sl(2g-2,\bar
Q_l)$ depending on whether C is hyperelliptic or not.
