Thank you all. Richard, this is referred to as embossing of leather. Its an ancient technique and is much like repousse on metal as it is formed from behind. It is fine tuned from the front. The cavity created is filled with leather shavings and hide glue.
JohnnyFM, What appears to look like the mermaid from an awful coffee company is actually Melucine, the woodland fairy from European folklore.
Her image is found in heraldic designs on tombstones, buildings and varying forms of art. Ken Gahagan found some of these while on a trip to Germany IIRC.
The late great Tom Curran also found multiple examples at the Met.
