Let D-L denote the class of bounded, simply connected real analytic plane d
omains with reflection symmetries across two orthogonal axes, of which one
has length L. Under generic conditions, we prove that if Ohm(1), Ohm(2) is
an element of D-L and if the Dirichlet, spectra coincide, Spec(Ohm(1)) = Sp
ec(Ohm(2)), then Ohm(1) = Ohm(2) up to rigid motion.