The tribe of Silmurry consisted of all the descendants of Muireadhach Muilleathan, with the major division in the tribe being between the descendants of Muireadhach's two sons, Ionnrachtach and Cathal. This webpage concerns the descendants of Cathal, known as Clann Cathail. The genealogy of the surnames descended from Ionnrachtach can be seen here.
The family groupings within Clann Cathail shown below are as listed in McFirbis' The Great Book of Irish Genealogies. Clann Cathail was ruled at various times by the O'Morans, O'Mulrenins, and the O'Flanagans, but the line of chiefs became permanent among the O'Flanagans by late medieval times. In addition to the family groupings below McFirbis lists 13 other surnames that he says also belonged to Clann Cathail: O'Mothlachain, O'Dathail, OhUllsa, O'Cloithfhilidh, O'Gusain, O'Fionnagain, O'Laighin, O'Laoghog, O'Tomhrair, O'Caomhoige, O'Breslein, O'Dubhain, and O'Fannain. He lists another sub-tribe in Clann Cathail called Siol Con Bhuidhe (a townland in Kilcorkey Parish called Ballyconboy was likely the land of that group). Other sources refer to O'Maolmordha (O'Moore) and O'Carthaig (O'Carthy) as being sub-chiefs of O'Flanagain.
The O'Flanagans had their main seat in Mantua (previously called Mointeach) which is located along the southern borders of Cloonyeffer and Corry East townlands in Shankill Parish. They also had another seat in the townland of Ballyroddy in Shankill Parish. They lost their territory to the O'Connor Roe in the 1300's.
A map of the approximate territory of Clann Cathail can be seen here.
