These cameos are lovely! The carving is exquisite, the colors of the natural shell are perfect, and the mountings are simple and subtle, yet rich, with an easy-to-match, latticework filigree.
Cameo is the art of carving a layered material, creating a portrait or landscape with a difference in colors. While traditionally done in shell, banded onyx has been used in cameo work - particularly in Greece and Italy - for hundreds, if not thousands, of years.
These have a smooth, undecorated earring post in 14k gold.?

Metal: 14k yellow gold
Gem: ?Cameo Natural Shell, likely conch
Gem Measurements 16 x 11 mm oval
Earrings Length: 28 mm
Earrings Width: 14 mm