Postby silvermakersmarks » Fri Jan 19, 2018 3:11 am
This is indeed an Irish mark and you have gone a fair way towards an identification. However I have to make one correction: the date is actually 1834 (the duty mark is the head of William IV who reigned until 1837). RG is, as you suggest, Richard Garde, a Cork silversmith. The harp is the Irish mark for sterling silver and Hibernia, at this period, was the mark of the Dublin Assay Office.
The engraving of the armoured arm holding an arrow is a family armorial; i.e. the symbol of the original owner. I believe that quite a few families used this but if you would like to while away a few hours you might like to browse through the book "Fairbairn's Crests", several editions of which are available online.
Phil