  Magnetic induction dependence of the dispersion of longitudinal
magnetoplasmon in a two-dimensional electron gas with finite layer thickness
under a static uniform magnetic field normal to the layer plane is calculated
using the self-consistent linear response approximation. Two longitudinal
magnetoplasmon modes are obtained. The calculated dispersion agrees with the
experiment by Batke {\it et al.} [Phys. Rev. B {\bf 34}, 6951 (1986)].
