  Tail emission of the prompt gamma-ray burst (GRB) is discussed using a
multiple emitting sub-shell (inhomogeneous jet, sub-jets or mini-jets) model,
where the whole GRB jet consists of many emitting sub-shells. One may expect
that such a jet with angular inhomogeneity should produce spiky tail emission.
  However, we found that the tail is not spiky but is decaying roughly
monotonically. The global decay slope of the tail is not so much affected by
the local angular inhomogeneity but affected by the global sub-shell energy
distribution. The fact that steepening breaks appeared in some events prefers
the structured jets. If the angular size of the emitting sub-shell is around
0.01-0.02 rad, some bumps or fluctuations appear in the tail emission observed
frequently in long GRBs. If the parameter differences of sub-shell properties
are large, the tail has frequent changes of the temporal slope observed in a
few bursts. Therefore, the multiple emitting sub-shell model has the advantage
of explaining the small-scale structure in the observed rapid decay phase.
