  We give positive descriptions for certain Schubert structure constants
$c_{u,v}^w$ for the full flag variety in Lie types $C$ and $D$. This is
accomplished by first observing that a number of the $K=GL(n,\C)$-orbit
closures on these flag varieties coincide with Richardson varieties, and then
applying a theorem of M. Brion on the decomposition of such an orbit closure in
the Schubert basis in terms of paths in the weak order graph.
