  We present evidence for a ring of stars in the plane of the Milky Way,
extending at least from l = 180 deg to l = 227 deg with turnoff magnitude $g
\sim 19.5$; the ring could encircle the Galaxy. We infer that the low Galactic
latitude structure is at a fairly constant distance of R = 18 +/- 2 kpc from
the Galactic Center above the Galactic plane, and has R = 20 +/- 2 kpc in the
region sampled below the Galactic plane. The evidence includes five hundred
SDSS spectroscopic radial velocities of stars within 30 degrees of the plane.
The velocity dispersion of the stars associated with this structure is found to
be 27 km/s at (l,b) = (198, -27), 22 km/s at (l,b) = (225, 28), 30 km/s at
(l,b) = (188, 24), and 30 km/s at (l,b) = (182, 27) degrees. The structure
rotates in the same prograde direction as the Galactic disk stars, but with a
circular velocity of 110+/-25 km/s. The narrow measured velocity dispersion is
inconsistent with power law spheroid or thick disk populations. We compare the
velocity dispersion in this structure with the velocity dispersion of stars in
the Sagittarius dwarf galaxy tidal stream, for which we measure a velocity
dispersion of 20 km/s at (l, b) = (165, -55) deg. We estimate a preliminary
metallicity from the Ca II (K) line and color of the turnoff stars of [Fe/H] =
-1.6 with a dispersion of 0.3 dex and note that the turnoff color is consistent
with that of the spheroid population. We interpret our measurements as evidence
for a tidally disrupted satellite of $2 \times 10^7$ to $5 \times 10^8 \rm
M_\odot$ which rings the Galaxy.
