Magnificent left-facing gold-filled shell cameo brooch/pendant

This vintage piece has rich detail in the carving and a finely detailed frame. The shell has a nice curve, giving the piece good neight. There is a bail that allows the piece to be worn as a pendant or a brooch. Measures 1-7/8 X 1-1/4 inches. I think some of the marking is not well stamped and it should read 12K GFCF 1/20, indicating 1/20 12K gold fill. The condition is excellent.