  We investigate the $D\bar{D}$ production in $e^+e^-$ annihilations near
threshold in an effective Lagrangian approach. This shows that the lineshape of
the cross section near threshold is sensitive to the contributions from
$\psi^\prime$, though it is below the $D\bar{D}$ threshold. The recent
experimental data from the BES and Belle collaborations allow us to determine
the $\psi^\prime D\bar{D}$ coupling constant which appears to be consistent
with other theoretical studies. As a consequence, the
$\psi^\prime$-$\psi(3770)$ mixing parameter can be extracted around the
$\psi(3770)$ mass region. Resonance parameters for $\psi(3770)$, X(3900),
$\psi(4040)$, and $\psi(4160)$ are also investigated. The X(3900) appears as an
enhancement at around 3.9 GeV in the Belle data. In addition to treating it as
a resonance, we also study the mechanism that the enhancement is produced by
the $D\bar{D^*}+c.c.$ open channel effects. Our result shows that such a
possibility cannot be eliminated.
