We are carrying out a sensitive blind survey for neutral hydrogen ( H i ) in the Virgo cluster and report here on the first 5 \degr \times 1 \degr area covered , which includes two optically-dark gas features : the five-cloud ALFALFA Virgo 7 complex \citep Kent2007 , Kent2009 and the stripped tail of NGC 4522 \citep Kenney2004 .
We discover a sixth cloud and low velocity gas that extends the velocity range of the complex to over 450 km s ^ { -1 } , find that around half of the total H i flux comes from extended emission rather than compact clouds , and see around 150 percent more gas , raising the total H i mass from 5.1 \times 10 ^ { 8 } M _ { \odot } to 1.3 \times 10 ^ { 9 } M _ { \odot } .
This makes the identification of NGC 4445 and NGC 4424 by \citet Kent2009 as possible progenitors of the complex less likely , as it would require an unusually high fraction of the gas removed to have been preserved in the complex .
We also identify a new component to the gas tail of NGC 4522 extending to \sim 200 km s ^ { -1 } below the velocity range of the gas in the galaxy , pointing towards the eastern end of the complex .
We consider the possibility that NGC 4522 may be the parent galaxy of the complex , but the large velocity separation ( \sim 1800 km s ^ { -1 } ) leads us to rule this out .
We conclude that , in the absence of any better candidate , NGC 4445 remains the most likely parent galaxy , although this requires it to have been particularly gas-rich prior to the event that removed its gas into the complex .