[en] An example of a rotating infinitely flattened self-gravitating particle system in steady state is considered. Non-stationary motion of the system in the neighborhood of this equilibrium solution is determined through the second-order perturbation. The first order perturbation terms give rise to a configuration of straight bars emanating from the center which become skewed under the influence of the second-order terms. In the case of a single bar, as in a barred spiral, the skewing is in the arms leading or arms trailing sense, according to whether the system is developing away from or approaching the equilibrium state. (Auth.)