62 
uneini are hooked and bluntly dentated. The anterior portion of 
the lingual ribbon is borne upon, and to a great extent surrounded 
by strong cartilages which give power and rigidity to the organ. 
At the tip the teeth are fully exposed, as from a sheath, and, 
being carried over the point of the cartilaginous support, some 
of the teeth project freely in front and form a powerful file 
bristling with sharp siliceous spines. When brought to bear upon 
the shells of other molluscs, and moved with regularity by the 
action of numerous muscles, a hole is speedily drilled, and the 
body of the helpless occupant devoured, or at least so much of it 
as suits the taste of the assailant, the residue being left to be 
cleared off by crabs or annelids. 
While operating, the boring mollusc is firmly fixed by its 
muscular foot to the shell of its victim, and the hole is drilled with 
the greatest precision and regularity. I am inclined to believe- 
that the cartilaginous sheath has a part to play in the perforation, 
but at present I am not able to say how, or to what extent. 
Oysters and mussels are commonly the victims of these marauding 
gasteropods, but, when hard pressed, they do not hesitate to prey 
on each other. 
The air breathing mollusca (Pulmonifera) afford examples of 
yet another form of dentition. The land snails and slugs, and the 
pond snails (Zimnea and Plunorbis) are familiar representatives of 
this order In these animals the lingual membrane is very broad, 
and is studded all over with small similar teeth, with broad bases, 
set in regular rows, like a pavement covering the floor of the 
mouth. Attached to the upper part of the mouth is a broad horny 
plate, against which the tongue can work. The lower edge of 
this plate is curved and sharply dentated, forming an upper 
mandible for cutting leaves, &c., while the minuter forms of vegeta- 
tion are appropriated by the scraping action of the odontophore, 
which can be protruded over the lip for that purpose. 
As might be expected, when we arrive at the highest order of 
mollusca——Cephalopoda, with their complicated and formidable 
_ instruments for seizing their prey, we find a proportionate advance 
in the dental apparatus. The mouth is situated in the centre of 
the disk from which the arms, with their prebensile suckers, 
radiate, and is surrounded by a broad fleshy lip. Within the 
orifice are a pair of strong hooked mandibles, not unlike the beak 
of a parrot. These are embedded in a mass of muscle, by means of- 
which they are opened and closed. Lying within the concavity, 
. formed by the horny jaws, is a fleshy tongue which, in this class, 
is supposed to be partly an organ of taste. A portion only of its 
surface is covered with teeth which serve to complete the comminu- 
tion of the food, already cut and torn by the mandibles, and to 
assist its passage to the esophagus. : 
7 
