Page:Natural History, Mollusca.djvu/230

218 or sandy mud, in from ten to one hundred fathoms;" but obtained most abundantly in from forty to seventy fathoms.

Dr. Gray remarks that the apices of the British specimens often appear to be either broken off, or to have fallen off of themselves, like the tips of those shells called decollated, as some of the Helicidæ; and he adds that when the tip is broken, the animal forms a slight tube within, which is more or less produced beyond the tip. Specimens in this condition have been described as distinct species. A parasitical worm, of the class Echinodermata, the Sipunculus Bernhardus, is frequently found inhabiting old and dead shells of the Dentalium, the mouth of which it closes, except a minute orifice, with a sort of mortar made with sand. This parasite has sometimes been mistaken for the original inhabitant of the shell.