  We present results of Monte Carlo calculations for the Lya line transfer in
an expanding dusty supershell, where Lya source is a well-localized star
cluster in a starburst galaxy.The escape of Lya photons from such system is
achieved by a number of back-scattering, and so a series of emission peaks are
formed redward of the systemic redshift by back-scattering. However, majority
of observed Lya emission from starbursts show singly-peaked asymmetric
profiles. We find in this paper that, in order to form a singly-peaked Lya
emission, dust should be distributed in the ionized bubble, as well as within
the supershell of neutral hydrogen. We also find that the overall escape
fraction of Lya photons is determined by the HI column density of the
supershell, the expansion velocity of the supershell, and the spatial
distribution of dust. However, the kinematic information of the expanding
supershell is preserved in the profile of Lya emission even when the supershell
is dusty. Our results are potentially useful to fit the P-Cygni type Lya line
profiles from starburst galaxies, either nearby galaxies or high-z Lyman break
galaxies (LBGs).
