THE SCREW SHELLS - TOWER SHELLS - FAMILY TURRITELLIDAE Shell a long slender spire of many whorls with revolving strim and fine, curved lines of growth; mouth oval, or four-angled; lip thin; operculum spiral, horny; head with broad snout; eyes on bases of long spreading tentacles; mantle edge fringed; gill plume long, single; foot short, truncate in front, narrowed behind, grooved underneath. A marine family.
Genus TURRITELLA, Lam.
Characters of the family. Four hundred fossil and one hundred living species, chiefly in the Old World. Very few on American beaches. A peculiarity of this genus is that the upper fourth of the shell is always empty and divided by a septum at each half-turn.
The Great Screw Shell (T. Cerebra, Linn.) has a most elegantly turned spire, tapering to a needle point, its sixteen whorls strongly grooved and ridged as if done in a lathe. The pale surface is stained with orange, or clouded all over with fulvous brown. The largest ones I have seen are five inches long, with a breadth at base of more than one inch. The same proportions hold in the smaller specimens. They come from the Philippine Islands.
The idea of the screw was suggested to the philosopher Archimedes by the spiral shell of Turritella terebra.
The Marbled Tower Shell (T. inarmoratus, Keiner) is an obelisk of many flattened whorls, finely marked with growth stria;. It tapers but little, and the apex is blunt. The surface is clouded and reticulated with lurid chocolate shades. Length,
6 to 8 inches.
The Variegated Tower Shell (T. variegata, Linn.) is clouded and streaked with chocolate colour upon a solid creamy white, china-like surface, and finely sculptured with revolving ridges. "Lady fingers" the children call these elegant shells which taper to a needle point. The sixteen flattened whorls are separated by narrow 'sinuses. Length, 21 to 5 inches.
Habitat.— Southern Florida, West Indies.