We report a search for narrow resonances, produced in p
anti-p collisions at s**(1/2) ñ.96 TeV, that decay into muon pairs
with invariant mass between 6.3 and 9.0 GeV/c2. The data, collected
with the CDF II detector at the Fermilab Tevatron collider, correspond
to an integrated luminosity of 630 pb-1. We use the dimuon invariant
mass distribution to set 90% upper credible limits of about 1% to the
ratio of the production cross section times muonic branching fraction
of possible narrow resonances to that of the Upsilon (1S) meson.