The Collaborative International Dictionary of English v.0.48:

Turritella \Tur`ri*tel"la\, n. [NL., dim fr. L. turris tower.]
   (Zool.)
   Any spiral marine gastropod belonging to Turritella and
   allied genera. These mollusks have an elongated, turreted
   shell, composed of many whorls. They have a rounded aperture,
   and a horny multispiral operculum.
   [1913 Webster]