  We construct a new variety of $N=2$ supersymmetric integrable systems by
junction of pseudo-differential superspace Lax operators for $a=4$, $N=2$ KdV
and multi-component $N=2$ NLS hierarchies. As an important particular case, we
obtain Lax operator for $N=4$ super KdV system. A similar extension of one of
$N=2$ super Boussinesq hierarchies is given. We also present a minimal $N=4$
supersymmetric extension of the second flow of $N=4$ KdV hierarchy and comment
on its possible integrability.
