  The level-spacing distribution of consecutive energy eigenvalues is
calculated numerically at the metal insulator transition for 3d systems with
different cuboid shapes. It is found that the scale independent critical
$P_c(s)$ changes as a function of the aspect ratio of the samples while the
critical disorder $W_c/V=16.4$ remains the same. We use our data to test
whether an expression for the small-$s$ behaviour of the level statistics
proposed by Kravtsov and Mirlin for the metallic regime is applicable also at
the critical point. For this reason, a shape dependent dimensionless critical
conductance $g_c$ has been extracted from the small-$s$ behaviour of the
critical level statistics. Our result for a cubic sample, $g_c=0.112\pm 0.005$,
is in good agreement with a value obtained previously from calculations using
the Kubo-formula.
