We derive a generalization of the well-known theorem for the square in
tegrability of a unitary irreducible representation of a locally compa
ct group. The generalization covers the case of representations admitt
ing vector coherent states. The result is illustrated by an example dr
awn from the isochronous Galilei group. The construction yields a wide
variety of coherent states, labeled by phase space points, which sati
sfy a resolution of the identity condition, and incorporate spin degre
es of freedom. (C) 1998 American Institute of Physics. [S0022-2488(98)
00108-X].