What is "cameo conch"

Cameo \Cam"e*o\ (k[a^]m"[-e]*[-o]), n.; pl. Cameos (k[a^]m"[-e]*[=o]z). [It. cammeo; akin to F. cam['e]e, cama["i]eu, Sp. camafeo, LL. camaeus, camahutus; of unknown origin.] A carving in relief, esp. one on a small scale used as a jewel for personal adornment, or like.

Note: Most cameos are carved in a material which has layers of different colors, such stones as the onyx and sardonyx, and various kinds of shells, being used. The classical cameos made in Italy are carved on a seashell (see cameo conch, below), having an olive figure carved from the inner layer of the shell in relief on the white background of the outer layer of the shell.

Cameo conch (Zo["o]l.), a large, marine, univalve shell, esp. Cassis cameo, Cassis rua, and allied species, used for cutting cameos. See Quern conch.

n. A large marine univalve shell, especially ''Cassis cameo'', ''Cassis rua'', and allied species, used for cutting cameos.