  We attribute the observed rotational velocity profiles of spiral galaxy disks
to a combination of Newtonian and exponential gravitational potentials. We
offer a novel, yet perfectly plausible, Lagrangian from which the exponential
potential is derived. The exponential potential is defined by two universal
constants (corresponding to a coupling constant and a graviton mass) that we
determine from our sample of 12 THINGS disks. All velocity profile fits are
excellent.
