  We present the results of a search for pair production of a new heavy
top-like quark t' decaying to a W boson and another quark using the CDF II
detector in Run II of the Tevatron proton-antiproton collider. Using a data
sample corresponding to 760 pb^-1 of integrated luminosity, we fit the observed
spectrum of total transverse energy and reconstructed t' quark mass to a
combination of standard model processes and t' pair production. We see no
evidence for t' pair production, and we infer a lower limit of 256 GeV/c^2 on
the mass of the t' at 95% C.L. assuming standard strong couplings for the t'.
