In respect to Delphi, they presumed that it was the umbilicus, or centre of the whole earth.
In this case the shell is said to be umbilicated, and the opening referred to is the umbilicus.
The shell is thick, imperforate (no umbilicus), and usually has flat, spiral ribs.
The other (T. zizyphinus) is usually of a yellowish or pink colour and has no umbilicus.
With umbilicus reaching to the apex; including Bifrontia and Orbis.
The umbilicus is partially closed by an entering callous plug.
At the end of it was the umbilicus urbis Romæ, or ideal center of the city and empire, the remains of which are recognizable.
In all the species of this genus there are one umbilicus and one cord.
It is in the region of the umbilicus, u, and the extreme caudal end of the stomach which has been called the gizzard, gz.
umbilicus—um-bĭ-līkus, according to Worcester, Thomas and Dunglison.
"navel," 1610s, from Latin umbilicus "navel," from PIE root *(o)nobh- "navel" (see navel). In English, mostly confined to medical writing. Latin umbilicus is source of Spanish ombligo as well as Old French lombril, literally "the navel," from l'ombril, which by dissimilation became modern Fr. nombril (12c.).
umbilicus um·bil·i·cus (ŭm-bĭl'ĭ-kəs, ŭm'bə-lī'kəs)
n. pl um·bil·i·ci (-sī')