Translation according to P. W. Joyce:
Ballygunneen in Galway; Baile-O'gCuinin, O'Cun-neeri's town. There is also a family name MacCunneenor Macunnin; but the 0 is detected in Ballygunneen by the eclipsis: see p. 10 [reproduced below].
Eclipsis caused by O in Gen. Plural. When an Irish family name with O is in the genitive plural, the O has the same effect as the article na - that is to say, it eclipses the word next following, which is the main family name here. Ballyogaha, in Cork, is Baile-O-gCathaigh, the town of the O'Cahas or O'Cahys, where the main family name comes out in anglicisation as O'Gaha instead of O'Caha.