Using the Beurling-Lax
description of invariant subspaces of H2(R), we describe the ideal structure of two
large classes of convolution algebras whose Fourier-Laplace Transforms are
entire functions. A closed ideal will be characlerized by its cospectrum or by
its cospectrum together with a nonnegative number related to the “rate of
decrease at infinity”; in the latter case, the closed ideals having the same
cospectrum form a totally ordered family {Iξ},ξ ∈ [0,∞), with Iξ⊋ Iη
whenever ξ < η. New examples of algebras to which the results apply are
given.