Denis O'Cullean explained

Denis O'Cullean (some sources O'Culean) was appointed Dean of Armagh^[1] in 1416^[2] and is recorded still in post in 1441.^[3]

References

1. "Fasti Ecclesiae Hibernicae: The succession of the prelates Volume 3" Cotton, H. p30 Dublin, Hodges & Smith, 1848-1878
2. http://www.stpatricks-cathedral.org/people/deans-of-armagh/ St Patrick's Cathedral, Armagh
3. http://www.ebooksread.com/authors-eng/james-b-leslie/armagh-clergy-and-parishes--being-an-account-of-the-clergy-of-the-church-of-ire-lse/page-3-armagh-clergy-and-parishes--being-an-account-of-the-clergy-of-the-church-of-ire-lse.shtml Armagh clergy and parishes : being an account of the clergy of the Church of Ireland in the Diocese of Armagh