Translation according to P. W. Joyce:
Knockogonnell in Clare and Galway; Cnoc-O'gConaill, hill of the O'Connells. C eclipsed after C in gen. plur.: 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.