This is a very late reply, but there's an actress named Gemma Jones in THE DEVILS. Maybe that's who you referred to?

She was in it. There is a pic floating around of her in the nude from it. She was devilishly hot.

I think you might be referring to the British movie "The Devils" with VANESSA REDGRAVE, a British actress. Carolyn Jones was not in that movie. I don't think she was in any horror film in the 70's but I may be wrong. She did the horror thriller "Eaten Alive" about a Louisiana bayou inn keeper who fed his hotel guests to a crocodile. I think she might have been in the horror film "Satan's School for Girls" in the early 70's but I'm not sure about that either. The Devils though was a very shocking movie for its time. That movie was about the 16th century Inquisition Days and a coven of nuns who become strangely possessed by the Devil. It's a graphic movie and very much earned either an R rating or X rating (at the time; this being a little before The Exorcist). I think the movie was released in 1970 or 1971.