This is a vintage Campagnolo Gran Sportrear derailleur - in good working condition, although one of the jockey wheels is a little stiff. Both appear original. States "DA 14 A 26 Denti" on rear. Probably from the mid-1950's.
Believed to be from a 1956 frameset and the front derailleur is also listed.
Comes with a bolt-on adaptor but it looks like that can be removed for a more modern hanger.
Happy to post, or can be collected from Dewsbury, West Yorkshire.