Dentalium

Dentalium is the genus which includes the common English "Elephant-Tusk Shell" (B. entale). This is a slender, curved, tubular shell, tapering gently to one end. It is about an inch or two in length. The shell is bright white, and resembles ivory in appearance; and its shape is like that of an elephant's tusk. The animal has a distinct "radula" or armed tongue, and so it belongs to the same group of Mollusca as the Gastropoda, the class which includes the ordinary univalve "shell-fish." It was once included in this class, but it differs from it in several very important points, such as the imperfect development of the head, and the absence of heart or distinct gills; hence it is now regarded as the type of a separate class, the Scaphopoda (q.v.). The animal burrows through sand, and is confined to a range of from 10 to about 100 fathoms. Dentalium has a great range in time, as it commenced in the Carboniferous system; it is now world-wide in distribution.