  We present the discovery of three faint dwarf galaxies and a globular cluster
in the halo of the Andromeda galaxy (M31), found in our MegaCam survey that
spans the southern quadrant of M31, from a projected distance of ~50 kpc to
\~150 kpc. Though the survey covers 57 sq. degrees, the four satellites lie
within 2\deg of one another. We estimate that the globular cluster lies at a
total distance of 175+/-55 kpc from M31, making it the farthest M31 globular
cluster known. It also shows the typical characteristics of a bright globular
cluster, with a half-light radius of 2.3+/-0.2 pc and an absolute magnitude in
the V band of M_{V,0}=-8.5+/-0.3 and contains a very old population with a
metallicity of [Fe/H]~-1.3. The three dwarf galaxies are all very faint, with
absolute magnitudes in the range -7.3<M_{V,0}<-6.4, and show strikingly similar
characteristics with metallicities of [Fe/H]~-1.4 and half-light radii of
\~120+/-45 pc, making these dwarf galaxies two to three times smaller than the
smallest previously known satellites of M31. We estimate them to be between 740
and 955 kpc from the Sun. Extrapolating from the coverage of the survey, we
estimate that up to 45+/-20 satellites brighter than M_V~-6.5 should be
orbiting M31. Hence faint dwarf galaxies cannot alone account for the missing
satellites that are predicted by $\Lambda$CDM models, unless they reside in
dark matter mini-halos that are more massive than the typical masse of 10^7
solar masses currently inferred from their central radial velocity dispersion.
(abridged)
