Vitalis and Agricola - A summary of what St. Ambrose says. - http://www.saintpatrickdc.org/ss/1104.htm#vita
St. Vitalis - Catholic Online seems to think that Vitalis was Agricola, or that the slave converted the master. - http://www.catholic.org/saints/saint.php?saint_id=1860
Sts. Vitalis and Agricola - This Vitalis was a slave, converted to Christianity by his master Agricola. Both were martyred at Bologna about 304. - http://www.newadvent.org/cathen/15486b.htm