In his book Surnames in Ireland,  Sean E Quinn (4)  has an entry for McCarron which may be the Donegal Anglicisation of Ui Mhic Carthainn.

McCarron, MaCearain, MacCiarain Page 55

A sept of Donegal derived from ciar meaning ‘black’. MacCarrghamhna (son of spear-calf), an ancient sept of Westmeath is sometimes so translated. In 1890 McCarron was principally found in Donegal and Derry, and the estimated number of bearers was 1,480.

His entry for McCartan is;

McCartan, Mac Artain page 56

A Gaelic sept meaning son of Artan (a diminutive of Art, an ancient word for bear). This sept were lords of Cinel Faghartaigh, now the barony of Kinelarty in Down. In 1890 McCartan was principally found in Down and Armagh, and the estimated number of bearers was 1,570.


Surnames in Ireland by Sean E Quinn ISBN 1 871 509 39 (4)