Mid-July, 1842. An English gentleman named “Dr. J. Griffin”, a member of the British Lyceum of Natural History, arrived in New York City bearing a remarkable curiosity — a real mermaid supposedly caught near the Feejee Islands in the South Pacific. The press were expecting him, since throughout the Summer they had been receiving letters from Southern correspondents describing the doctor and his mermaid. So when he checked in to his hotel, reporters were waiting for him, demanding to see the mermaid. Grudgingly he obliged. What they saw totally convinced them of the creature’s authenticity.
It's a pretty gruesome creation, right? P.T. Barnum earned a small fortune and created a sensation with this beast.
The Museum Of Hoaxes tells the full story, but it begins like this:
You will have to go to the link to get the rest, but suffice it to say that the term Feegee Mermaid now covers all such hoaxes.