  The Arecibo Dual-Beam Survey is a "blind" 21 cm search for galaxies covering
\~430 deg^2 of sky. We present the data from the detection survey as well as
from the follow-up observations to confirm detections and improve positions and
flux measurements. We find 265 galaxies, many of which are extremely low
surface brightness. Some of these previously uncataloged galaxies lie within
the zone of avoidance where they are obscured by the gas and dust in our
Galaxy. 81 of these sources are not previously cataloged optically and there
are 11 galaxies that have no associated optical counterpart or are only
tentatively associated with faint wisps of nebulosity on the Digitized Sky
Survey images. We discuss the properties of the survey and in particular we
make direct determinations of the completeness and reliability of the sample.
The behavior of the completeness and its dependencies is essential for
determining the HI mass function. We leave the discussion of the mass function
for a later paper, but do note that we find many low surface brightness
galaxies and 7 sources with M_HI < 10^8 Msolar.
