Hi Guys,
sorry to say this is a very well made mold. I have the same piece & bought it 25 years ago in a Paris flea market. I was sure it was the real deal back then. After some research I have seen a dozen examples & this description:
It is sometimes called "fakeshaw"
"This is a well-known fake of a scrimshawed sea turtle shell. It is NOT a replica or reproduction, because no original ever existed. The image was designed by a master mold-maker of the Juratone Company of London, England. The image as well as the shell joints were part of a mold, into which liquid plastic was poured. Hundreds, if not thousands of identical copies were made and sold by Juratone. The fake is very heavy, and freight costs more than the plastic is worth"