Note:  Do not rely on this information. It is very old.

Melusina

Melusina, or Melusine, a fairy of French romance, daughter of the fairy Pressina and Elenas, King of Albania. She was the wife of Raymond, Count of Poitiers. Owing to a malignant charm she used to become a serpent from the waist downwards every Saturday. On discovering this, her husband imprisoned her in a dungeon of the castle of Lusignan, where traditions of her still survive.