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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 

 m n*e 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, 



