  If the Dark Matter consists of primordial black holes (PBHs), we show that
gravitational lensing of stars being monitored by NASA's Kepler search for
extra-solar planets can cause significant numbers of detectable microlensing
events. A search through the roughly 150,000 lightcurves would result in large
numbers of detectable events for PBHs in the mass range $5 \ten{-10}\msun$ to
$\aten{-4}\msun$. Non-detection of these events would close almost two orders
of magnitude of the mass window for PBH dark matter. The microlensing rate is
higher than previously noticed due to a combination of the exceptional
photometric precision of the Kepler mission and the increase in cross section
due to the large angular sizes of the relatively nearby Kepler field stars. We
also present a new formalism for calculating optical depth and microlensing
rates in the presence of large finite-source effects.
