Prince of Conmaicne or Conmhaicne

The Conmaicne of Magh Réin were found in northwest Connacht (southern Co. Leitrim) in the territory of Bréifne. The Conmaicne Réin were chiefly divided among three clan groupings - Muintir Eolais, Cenel Luachain and Muintir Cearbhallain. Of particular note was the powerful Muintir Anghaile (O'Farrell of Annaly, co. Longford) who are also claimed to descend from the Conmaicne Réin.

The Conmhaicne or Conmaicne were an ancient tribal grouping that were divided into a number of distinct branches that were found scattered around Ireland in the early medieval period. They settled in Connacht, where they gave their name to several territories.
Their name came from a mythical ancestor known as Conmac. Conmac was in turn said to be descended from Fergus mac Roich and Queen Maeve of Connacht. The word Conmacne means "progeny of Conmac" (ne, a progeny). Conmac itself means "hound-son" (con, hound; mac, son).  https://en.wikipedia.org/wiki/Conmhaícne

Conmaicne Maigh Rein, or Conmaicne Rein na bFomorach, County Longford and south County Leitrim

Conmaicne Réin - part of Breifne in southern Co. Leitrim. The Conmaicne Réin were chiefly divided among three clan groupings - Muintir Eolais (e.g. MacRannall, Reynolds), Cenel Luachain (e.g. MacDorcy) and Muintir Cearbhallain (e.g. O'Mulvey). The early genealogies cite 'Finer' as the son of Cúscraid macCécht as, a quo Conmaicne Réin of Bréifne. They further cite Cairpre [of the] Conmaicnib Réin, that is Carpre mac Ailella (?Carpri Filed, son of Ailella Máir, in descent from Dáire Barraich mac Cathaír). The O'Rourkes were over-lords in this area for many centuries.

The Annals cite :

• For 1065, Duarcán, mac Maoil Mhiadhaigh Uí Eolusa, toiseach Muintire Eolais.
• For 1078, Domnall mac Tigernain h-Úi Ruairc, rí Conmaicne.
• For 1085, Muiredhach mac Duibh, toisech Muintire Eolais.
• For 1087, Airt Uí Ruairc, tigherna Conmaicne & Breifne.
• For 1087, Muiredhach mac Duibh, toiseach Muinntire h-Eolais.
• For 1101, Donnchadh, mac Airt Uí Ruairc, rí h-Úa m-Briuin & Conmaicne, died.
• For 1102, Domhnall, mac Tighernáin Ui Ruairc, rí Connacht & h-Ua Bríuin & Conmaicne.
• For 1125, Tigernan h-Úa Ruairc, rí h-Úa m-Briuin & Conmaicne.
• For 1139, Ferghal, mac Raghnaill, mic Muiredhaigh, taoiseach Muintire h-Eolais was slain by Tigernan h-Úa Ruairc.
• For 1150, Conchobhar Mac Raghnaill, tigherna Muintire h-Eolais.
• For 1167, Conn Ua Maoil Mhiadhaigh, toiseach Muintire h-Eolais.
• For 1169, Raghnall Ua Maoil Mhiadhaigh, toiseach Muintire Eolais.
• For 1171, Tigernan h-Ua Ruairc, ri Breifne & Conmaicne.
• For 1171, Aedh h-Ua Ruairc, rí Machaire Gaileng & ridomna h-Ua Briuin & Conmaicne.
• For 1179, Melaghlin O'Mulvey, Chief of Muintir-Eolais, died.
• For 1179, Raghnall, mac Mic Raghnaill, toiseach Maintiri h-Eolais.
• For 1196, The chiefs of Muintir-Eolais were treacherously slain by the son of Cathal O'Rourke. Murray Mac Rannall, surnamed the Gillaroe, Chief of Muintir-Eolais, was slain by the son of Manus O'Conor, at the instigation of the son of Cathal O'Rourke, who had procured the deaths of the above-mentioned chiefs.

For further reference in the annals, see Conmaicne Réin of Breifne.