216 PECTINIBRANCHIATA.—DENTALIADA. 
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protruded or withdrawn at the pleasure of the 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. 
Genus DENTALIUM. 
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 
branchie, 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 
