  We consider the (projective) representations of the group of holomorphic
automorphisms of a symmetric tube domain $V\oplus i\Omega$ that are obtained by
analytic continuation of the holomorphic discrete series. For a representation
corresponding to a discrete point in the Wallach set, we find the decomposition
under restriction to the identity component of $GL(\Omega)$. Using Riesz
distributions, an explicit intertwining operator is constructed as an analytic
continuation of an integral operator. The density for the Plancherel measure
involves quotients of $\Gamma$-functions and the $c$-function for a symmetric
cone of smaller rank.
