  In Debattista et al. (2015), we proposed that a kiloparsec-scale nuclear disc
is responsible for the high-velocity secondary peak in the stellar
line-of-sight velocity distributions (LOSVDs) seen at positive longitudes in
the bulge by the Apache Point Observatory Galactic Evolution Experiment
(APOGEE). Here, we make further qualitative but distinctive predictions of the
kinematic properties of a nuclear disc, including for the LOSVDs at negative
longitudes (which APOGEE-2 will observe) and examine the proper motions
throughout the disc. Since a nuclear ring is also able to produce similar
high-velocity LOSVD peaks, we present predictions for the proper motion
signatures which distinguish between a nuclear disc and a nuclear ring. We also
demonstrate that the stars in a nuclear disc, which would be on x2 orbits
perpendicular to the bar, can remain on these orbits for a long time and can
therefore be old. We show that such (old) nuclear discs of comparable size
exist in external galaxies.
