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CHAPTER V. 
DESCRIPTION OF BIVALVE SHELLS. 
Foremost among bivalves is the oyster, the bi- 
valve par excellence . Its praises have been sung 
for centuries, and we fancy it will be more and 
mire sought for, till the end of time. Its delicate, 
albuminous structure, its nutritious juices, and 
its delicious flavor have made it a favorite dish, 
at least from the time of the Romans ; and at 
the present time great numbers of men find em- 
ployment in propagating these mollusks, and 
preparing them for the table. 
For study, large oysters can easily be obtained, 
end an examination of their organs will give a 
key to the anatomy of many other genera. The 
ligamental cavity, the single muscular impress- 
ion, and the structure of the hard layers can 
easily be studied from the dry shell, while the 
thin mantle, long, comb-like gills, triangular lips, 
and sack-shaped heart can be seen by carefully 
dissecting a specimen which has been killed by 
immersing it for some time in fresh water. An 
excellent little guide for such study is published 
by Ginn and Heath, of Boston. 
Our common Oregon species, Ostrea lurida , 
Cpr., is the chief native oyster. It is small, thin, 
