Concha

(lit. a muscle or cockle). (1) A shell or shell-fish. (2) A Triton’s conch. In works of art, the Triton, or sea-god, has for a trumpet the buccina, remarkable for a spiral twist, long and straight; or the murex, equally twisted, but short and wide-mouthed. (3) The term was applied, by analogy, to various objects having the shape of a shell, such as cups or vases used for holding perfumes or for other purposes. (4) In Architecture, an apse, or a plain concave of a dome, is so called.