Strange you should mention it. The other day I went looking and found this site which is as coincidental as a very coincidental thing (which form of phrase incedentaly originates AFAIK from a Wonderstuff song on the Eight Legged Groove Machine album).
Sooooo....five D tribes then, and only the Durotriges (Roman name) that I'd heard of.
Segontium is the name for the Roman fort at Caernarfon btw.
If you don't look at the site...
This is relevant because there was a tribe called the Segontiaci by the Romans that lived there.