THE SHELL It is a conical tube spirally wound to the right about a central axis, the columella. The closed, pointed end is the apex; the coiled whorls form the spire. The last coil is called the body whorl, for in it the body lies. The spout-like prolongation is the anterior canal. The spiral channel is the suture. The shell's mouth is called the aperture. The outer lip is opposite the columella, or inner lip. Lines of growth cross the whorls, close together, and parallel to the outer lip. The hairy skin covering the shell when it is alive is the epidermis. Lining the interior is the enamel. Between these is the main shell substance composed chieflyof lime.
When the body is drawn into the shell the aperture is closed by a horny door, the operculum.
Hold the spiral shell of the conch by its long stem, the an terior canal; the apex is pointed upward; the aperture is at the right. The anterior parts of the body reach the aperture; the posterior parts extend towards the apex. The ventral part of the body is underneath when the foot is extended. It is the inner, short side of the coil. The dorsal part is the arch of the body, the long, outer side of the coil. These terms are necessary to designate the relative positions of the internal organs.