Abstract. Let (B, R, α) be a C * -dynamical system and let A = B α ([0, ∞)) be the analytic subalgebra of B. We extend the work of Loebl and the first author that relates the invariant subspace structure of π(A), for a C * -representation π on a Hilbert space Hπ, to the possibility of implementing α on Hπ. We show that if π is irreducible and if lat π(A) is trivial, then π(A) is ultraweakly dense in L(H π ). We show, too, that if A satisfies what we call the strong Dirichlet condition, then the ultraweak closure of π(A) is a nest algebra for each irreducible representation π. Our methods give a new proof of a "density" theorem of Kaftal, Larson, and Weiss and they sharpen earlier results of ours on the representation theory of certain subalgebras of groupoid C * -algebras.