"The beak is the lengthened process (g) at the lower part of the shell.
"The canal, or gutter, runs through the beak. (Both these parts are perceptible in Murex and Strombus, [Plate 7].)
"Sutures are spiral lines which separate the whorls; they are sometimes crenated, or notched, sometimes sulcated, or furrowed.
"The columella, or pillar, extends through the centre of the shell withinside. The Buccinum and Voluta both show the columella. ([Plate 3.])
TERMS—
UNIVALVES.
"The pillar-lip of the aperture, or columella margin, is on the left-hand side of the shell; the outer lip on the right-hand. Occasionally this order is reversed, but not commonly.
"The operculum, or lid, in univalves is that part which fits exactly into the aperture, and incloses the animal; it serves as a door to the shell. ([Plate 3.]) The operculum is either horny, like that of the periwincle, or of a harder substance, like the shell itself.
"The umbilicus is a circular hole in the body of the shell. This perforation produces a very curious effect when it is very large. When the umbilicus is wanting, the shell is called imperforate.
"If the spire is truncated, it is decollated; if it is surrounded with spires, it is coronated, or crowned.