The Solar Neighborhood. XVIII. Discovery of new proper motion stars with 0.40 arcsec yr^-1 > mu >= 0.18 arcsec yr^-1 between declinations -90 degrees and -47 degrees

We report 1606 new proper motion systems in the southern sky (declinations -90 degrees to -47 degrees with 0.40 arcsec yr^-1 > mu >= 0.18 yr^-1. This effort is a continuation of the SuperCOSMOS-RECONS (SCR) proper motion search to lower proper motions than reported in Papers VIII, X, XII, and XV in this series. Distance estimates are presented for the new systems, assuming that all stars are on the main sequence. We find that 31 systems are within 25 pc, including two systems -- SCR 0838-5855 and SCR 1826-6542 -- we anticipate to be within 10 pc. These new discoveries constitute a more than ten-fold increase in new systems found in the same region of sky searched for systems with mu >= 0.40 arcsec yr^-1, suggesting a happy hunting ground for new nearby slower proper motion systems in the region just north (declinations -47 degrees to 0 degrees, much of which has not been rigorously searched during previous efforts.