The Irish Clan was a clan of gargoyles that lived in Ireland in ancient times. 
Sometime around the first century AD, the Hound of Ulster came from the Irish Clan, and it seems likely that at that time Cu Chullain knew of them as well.
Their protectorate (besides their own rookery) and their connection (if any) to other local people (for example, humans or Sidhe) are unknown.
By 1996, the Irish Clan was extinct, and had probably been destroyed by humans centuries (if not millennia) before then. 
All that is known about the physical characteristics of this clan is that they are likely somewhat Celtic in appearance. 
The Hound of Ulster - A gargoyle beast member of the clan at some point around the first century AD.