Gilla na Naemh Crom Ó Seachnasaigh, Chief of the Name, died 1224.
Ó Seachnasaigh was lord of Cenél Áeda na hEchtge, but is only recorded in the Irish annals towards the end of his era.
Only three more Ó Seachnasaigh's would be named in the annals before the 16th century (1240, 1403, 1408), none of them chiefs. Thus the succession of the lordship is unclear till c. 1533.
References
Gilla na Naemh Crom Ó Seachnasaigh Wikipedia(Text) CC BY-SA