The animal is attached to its shell only at its posterior end; the fore parts are capable of being protruded or withdrawn at the pleasure of the animal. When fully expanded the foot is thrust out in the form of a thickened and pointed tongue, surrounded by a trumpet-like lobe; the whole of which has been compared to the expanded corolla of a flower, with a very thick and pointed pistil.
As the family includes but this one genus, it is needless to repeat the characters by which it is distinguished. The species are rather numerous; M. Deshayes enumerates twenty-three living and thirty-four fossil, and several have been added to both lists since he wrote. Their geographical distribution is extensive, few seas being without some representatives of the genus; and they range from deep water to within tide-marks. In their habits they are carnivorous, feeding on those minute animals with chambered shells called Foraminifera, as well as on small bivalves. Mr. Clark has found species of as many as eleven distinct genera in the pouches on the two sides of the mouth, or in the stomach, of our commonest Tusk-shell (Dentalium Tarentinum). The same acute naturalist has the following observations on the affinities of the genus, already slightly alluded to:—
"The symmetrical, subventral position of the branchiæ, the posterior flow of water to them, and the resemblance of the foot to that of some of the bivalves, combined with the similar character of its action, appear in a striking manner to show its connexion with the Conchifera: whilst by its