  Following recent evidence that the vortices in decaying two-dimensional
turbulence can be classified into small--mobile, and large--quasi-stationary,
this paper examines the evidence that the latter might be considered a
`crystal' whose formation embodies the inverse cascade of energy towards larger
scales. Several diagnostics of order are applied to the ostensibly disordered
large vortices. It is shown that their geometric arrangement is substantially
more regular than random, that they move more slowly than could be expected
from simple mean-field arguments, and that their energy is significantly lower
than in a random reorganisation of the same vortices. This is traced to
screening of long-range interactions by the preferential association of
vortices of opposite sign, and it is argued that this is due to the mutual
capture of corrotating vortices, in a mechanism closer to tidal disruption than
to electrostatic screening. Finally, the possible relation of these `stochastic
crystals' to fixed points of the dynamical system representation of the
turbulent flow is briefly examined.
