324 
THE OCEAN WORLD. 
us to describe a few families, or rather types of families, such as th e 
Oyster, Ostrea; the Mussel, Mytilus ; the Tridacna; the Cockl e > 
Car dium ; and the Ship Worm, Teredo. 
1. The Ostreadie form a small group of Acephalous Mollusc®, 
which includes the Oyster, Ostrea spondylus, the Peciens, th e 
Hammerheads, Malleus, and the Pintadines, Meleagrina. 
2. The Mytiijdjs or Mussels are the type of another family) 
among which the ham -shaped Pinna, the Anodonta, and TJnio, 
the most remarkable members. 
3. The Tridacna stand alone and unrivalled in respect to size ’ 
being much used in Homan Catholic churches to hold the holy watei , 
hence their French name Benitier. 
4. The Yeneredie (Cockles) constitute with Donax, Tellina , a B 
Venus one important family. 
5. The Pholad.® (Borers) are a redoubtable family of destroyer®' 
of which the Teredo, Solen, and Pholas are distinguished members. 
OsTBEADiE. 
The shell of the oyster we need not dwell upon; it is the o"° 
bivalve universally known. It is unequally valved, modified in sh»F 
by the form of the submarine body to which it happens to be attache • 
The lower or adherent valve is concave, always the largest ; the upp e * 
one thin, usually flat ; the shell is lamellar, rough externally, ^ 
seems to be composed of broken leaves, adhering slightly to 
other, as if the successive leaves had been built up from within, arl 
each succeeding layer was an enlargement upon its predecessor, 
hinge which unites the valves is an elastic toothless ligament pl a ° e 
behind the centre, which opens the valves. 
The interior surface of the valves is smooth and white, diaphan 0 ^ 
or pearly towards the centre, but near the back an oval or roundf 
impression may be observed, to which a thick and whitish fleshy b° • 
is attached. , This is the central muscle which draws the valves tog e 
ther, hermetically closing them upon the animal. This muscle is c 
through in the process of opening the oyster. 
The animal has no power of locomotion ; its foot is very small a® 
often wanting, no syphon, but lies with its mouth open, and shg 1 ^ 
attached to the shell. The shell itself is always adherent, as H b ° 
