  Using the catalog of O'Neil, Bothun, & Schombert (1999), we examine the
central surface brightness distribution (phi(mu_B(0))) of galaxies in the 22.0
< mu_B(0) < 25.0 mag arcsec^{-2} range. Taking advantage of having a catalog in
which each galaxy has a known central surface brightness, scale length, and
redshift, we apply a bi-variate volume correction to the data and extend the
surface brightness distribution function by one magnitude, to 25.0 B mag
arcsec^{-2}. The result is a flat (slope = 0) surface brightness distribution
function from the Freeman value of 21.65 +/- 0.30 to the survey limit of 25.0
mag arcsec^{-2}, more than 11 sigma away. This indicates that a significant
percentage of the baryonic content of the universe is likely in potentials only
dimly lit by the embedded galaxy.
