  We investigate $J/\psi$ suppression in ultrarelativistic heavy ion collisions
within a generalized GLAUBER model and compare results of a hadronic comover
scenario with those of a quark plasma scenario where conditions for MOTT
dissociation of charmonium are fulfilled locally at the short time scales
before hadronization. We study possible consequences for the theoretical
description to be drawn from the observation of ``anomalous'' thresholds in the
$J/\psi$ suppression pattern by the NA50 collaboration.
