"As surnames were not generally used, either in Ireland or
anywhere else, till after the 10th century, the great families
are distinguishable at first only by their tribe or clan
names. Thus, at the north we have the Hy-Nial race; in the
south the Eugenian race, so called, from Nial and Eoghan,
their mutual ancestors."
_T. D. McGee,
Popular History of Ireland,
book 1, chapter 2 (volume 1)._