This antique carnelian carved intaglio fob depicts Medusa.
It is mounted in what we assume is a gold filled surround (it does not acid test as 10K gold and do not have a means of testing below that).
The fob measures 1 1/4" (includes bail and top mount) x 3/4". As you will see in the photos, the intaglio displays several chips around the edges. Fortunately, the image of Medusa remains intact.