  Within the framework of the instantaneous Bethe-Salpeter equation, we present
a detailed analysis of light meson spectra with respect to various
parameterizations of confinement in Dirac space. Assuming a linearly rising
quark-antiquark potential, we investigate two different spinorial forms (Dirac
structures), namely ${1/2}(\Id\otimes\Id - \gamma^0\otimes\gamma^0)$ as well as
the $U_A(1)$-invariant combination ${1/2}(\Id\otimes\Id -
\gamma^5\otimes\gamma^5 - \gamma^\mu\otimes\gamma_\mu)$, both providing a good
description of the ground state Regge trajectories up to highest observed
angular momenta. Whereas the first structure is slightly prefered concerning
numerous meson decay properties (see \cite{pap41}), we find the
$U_A(1)$-invariant force to be much more appropriate for the description of a
multitude of higher mass resonances discovered in the data of the {\sc Crystal
Barrel} collaboration during the last few years. Furthermore, this confinement
structure has the remarkable feature to yield a linear dependence of masses on
their radial excitation number. For many experimental resonances such a
trajectory-like behaviour was observed by Anisovich {\it et al.} We can confirm
that almost the same slope occurs for all trajectories. Adding the
$U_A(1)$-breaking instanton induced 't Hooft interaction we can compute the
pseudoscalar mass splittings with both Dirac structures and for the scalar
mesons a natural mechanism of flavour mixing is achieved. [...]
