We present results of a blind 21cm H I -line imaging survey of a galaxy overdensity located behind the Milky Way at \ell,b \approx 160 ^ { \circ } , 0.5 ^ { \circ } .
The overdensity corresponds to a Zone-of-Avoidance crossing of the Perseus-Pisces Supercluster filament .
Although it is known that this filament contains an X-ray galaxy cluster ( 3C 129 ) hosting two strong radio galaxies , little is known about galaxies associated with this potentially rich cluster because of the high Galactic dust extinction .
We mapped a sky area of \sim 9.6 sq.deg using the Westerbork Synthesis Radio Telescope in a hexagonal mosaic of 35 pointings observed for 12 hours each , in the radial velocity range cz = 2400 - 16600 km s ^ { -1 } .
The survey has a sensitivity of 0.36 mJy/beam rms at a velocity resolution of 16.5 km s ^ { -1 } .
We detected 211 galaxies , 62 % of which have a near-infrared counterpart in the UKIDSS Galactic Plane Survey .
We present a catalogue of the H I properties and an H I atlas containing total intensity maps , position-velocity diagrams , global H I profiles and UKIDSS counterpart images .
For the resolved galaxies we also present H I velocity fields and radial H I surface density profiles .
A brief analysis of the structures outlined by these galaxies finds that 87 of them lie at the distance of the Perseus-Pisces Supercluster ( cz \sim 4000 - 8000 km s ^ { -1 } ) and seem to form part of the 3C 129 cluster .
Further 72 detections trace an overdensity at a velocity of cz \approx 10000 km s ^ { -1 } and seem to coincide with a structure predicted from mass density reconstructions in the first 2MASS Redshift Survey .