Horniman museum has a mermaid

If you want to visit a Feejee mermaid, they have one at the Horniman Museum in London. It's been CAT-scanned and otherwise investigated. You can read about it

at the Guardian,

and also on the Horniman Museum's website itself.

A longer article from the Journal of Museum Ethnography can be downloaded from here.

A rather similar creature, CC image from the Wellcome Trust