Actually, remaining Celtic languages are divided into two categories, Gaelic and Brythonic. Irish, Max and Scots Gaelic are in the Gaelic category; Welsh, Cornish and the language spoken in Brittany are in the Brythonic. Gaelic is thought to be the more ancient of the two divisions.
Maybe that chart I linked to in post 36 is a little out of date. It is a neat way to show the language explosion though, and the relationships between modern, ancient, and inferred languages.