  We examine the severe disagreement between the number of predicted and
observed pulsation modes for Delta Scuti stars. The selection of nonradial
modes trapped in the outer envelope is considered on the basis of kinetic
energy arguments. The trapped l=1 modes for the star 4 CVn are in good, but not
perfect agreement with the observations. The trapping of the l=2 modes is
weaker, so that this simple rule of mode selection may apply to l=1, and
possibly not to l=2 modes.
