We study matrix string scattering amplitudes and matrix string instantons o
n a marked Riemann surface in the limit of a vanishing string coupling cons
tant. We give an explicit parameterization of the moduli space of such inst
antons. We also give a description of the set of fermionic supermoduli. The
integration over the supermoduli leads to the inclusion of picture changin
g operators at the interaction points. Finally we investigate the large-N l
imit of the measure on the instanton moduli space and show its convergence
to the Weil-Petersson measure on the moduli space of marked Riemann surface
s.