Interesting question, Sigured. There's a bit on the 1798 Homepage. Another little smidgeon I found was that Shelmalier referred to the "Wexford fishermen who became gunmen in the Irish rising of 1798." You'll also find a bit of mention here (click). I take it that Shelmalier is a Barony in County Wexford in the southeast corner of Ireland, but it isn't on any of my maps. This site says

The journey to Wexford by road or river has many pleasant views, and some bends of the river are particularly lovely. The last stages lie through the Barony of Shelmalier, which has always had a population of net-fisherman and fowlers. The ?bold Shelmalier?, with his long-barrelled duck-gun, was a formidable marksman in the Wexford insurgent army. He is commemorated in many ballads.

Well, that's what I was able to glean. I'm sure we'll have some Ireland experts who will be able to give us much more.
-Joe Offer-