THE SHELL-FISH OF THE COAST. 45 



OYSTERS, SCALLOPS, MUSCLES, AND ARKS. 



The oyster is so familiar to everybody that it 

 scarcely needs description. Still, there are a num- 

 ber of points connected with its structure and his- 

 tory which may not be generally known, and may 

 consequently be touched upon with advantage. In 

 the first place, let it be said that there are two gen- 

 erally recognized species or varieties on our coast, 

 — one known as the Virginia oyster, of an elongated 

 form, and the other, deeply scalloped, the ITorthern 

 oyster (Osirea borealis). But the shell of the oyster 

 varies so greatly, depending for its form so much 

 upon the shape of the object upon which it immov- 

 ably attaches itself in later life, that it becomes a 

 matter of great difficulty to determine the proper 

 limits of specific variation ; and, indeed, as far as 

 the two forms above noted are concerned, it is very 

 doubtful if they do not in reality belong to a single 

 species. In both, as in nearly all oysters, the left 

 valve is the larger of the two, and it is upon this 

 that the animal rests. The two are brought to- 

 gether by means of a single powerful muscle (ad- 

 ductor), whose attachment to the shell leaves the- 

 dark sub-central impression which is frequently 

 called the ' heart' 



Oysters are marine in habit, but they seem able 

 to endure a certain amount of exposure to fresh 

 water, as in the mouths of estuaries and bays, 

 which constitute their chief abiding-place. The 

 ' banks' or ' reefs' rise to within a few feet of the 

 surface, and in many regions are even exposed 



