  We derive a simple, closed form expression for the potential of a thin
exponential disk of stars interacting through gravitational potentials of the
form $V(r)=-\beta /r+\gamma r/2$, the potential associated with fundamental
sources in the fourth order conformal invariant theory of gravity which has
recently been advanced by Mannheim and Kazanas as a candidate alternative to
the standard second order Einstein theory. Using the model, we obtain a
reasonable fit (flat to within $\pm3\%$) to the (prototypical) NGC3198 $HI$
rotation curve data without the need for any non-luminous or dark matter. Our
study suggests that th observed flatness of rotation curves may only be an
intermediate phenomenon, and an asymptotic one.
