In American crime movies, Italians are called either guineas or ginnys (I'm not sure of the spelling

In American crime movies, Italians are called either guineas or ginnys (I'm not sure of the spelling). What's the origin of this derogatory term?

• Guinea "derogatory term for Italian" (by 1896) was originally Guinea Negro entymonline.com says: "(1740s) and meant "black person, person of mixed ancestry." It was applied to Italians c.1890 probably because of their dark complexions relative to northern Europeans, and after 1911 was occasionally applied to Hispanics and Pacific Islanders as well." Robert De Niro says in Goodfellas "the Irishman's here to take you guineas money." I say can't we all play nicely?

  Danny, Palermo, Italy