  We consider a class of shell models of 2D-turbulence. They conserve
inertially the analogues of energy and enstrophy, two quadratic forms in the
shell amplitudes. Inertially conserving two quadratic integrals leads to two
spectral ranges. We study in detail the one characterized by a forward cascade
of enstrophy and spectrum close to Kraichnan's $k^{-3}$--law. In an inertial
range over more than 15 octaves, the spectrum falls off as $k^{-3.05\pm 0.01}$,
with the same slope in all models. We identify a ``spurious'' intermittency
effect, in that the energy spectrum over a rather wide interval adjoing the
viscous cut-off, is well approximated by a power-law with fall-off
significantly steeper than $k^{-3}$.
