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It is shown that the discrepancy between the measured rate for $'+Xoy and that predicted by nonrelativistic models can be accounted for by ( v / c )~ relativistic corrections. A Breit-Fermi Hamiltonian is used to predict the energy level structure and E 1 transition rates in the charmonium and Y systems. It is obtained from an instantaneous approximation to a Bethe-Salpeter equation whose kernel is composed of Coulomb-gauge gluon exchange and a scalar confining piece. The model accounts for the observed fine and hyperfine structure of the charmonium levels and for the E 1 transition rates. It is used to predict the level structure and E 1 rates in the Y system. It is shown that an extension of Siegert's theorem is valid in the relativistic regime. This result is useful in analyzing E 1 transition-matrix elements.

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