Two versions of the opening argument:
1798: THE RIME OF THE ANCYENT MARINERE, IN SEVEN PARTS ARGUMENT. How a Ship having passed the Line was driven by Storms to the cold Country towards the South Pole; and how from thence she made her course to the tropical Latitude of the Great Pacific Ocean; and of the strange things that befell; and in what manner the Ancyent Marinere came back to his own Country. Becomes in 1800: The Ancient Mariner. A Poet's Reverie. How a Ship, having first sailed to the Equator, was driven by Storms, to the cold Country towards the South Pole; how the Ancient Mariner cruelly, and in contempt of the laws of hospitality, killed a Sea-bird; and how he was followed by many and strange Judgements; and in what manne he came back to his own Country.
Here is a link to more information & the poem: http://etext.lib.virginia.edu/stc/Coleridge/stc.html
ps. I do not see the epigraph in our edition in either the 1798 or the 1800. I suspect it was added in 1817, but have not verified this.