OSTREA EDULIS. 



coarsely laminated. Left or inferior valve adherent, largest 

 and deepest ; its summit prolonged by age into a kind of 

 keel. Right or upper valve smallest, more or less operculi- 

 form. Hinge oral, toothless. Ligament somewhat internal, 

 short, inserted in a cardinal pit, growing with the summit. 

 The muscular impression unique and subcentral. 



THE SPECIFIC CHARACTERS. 



OSTREA EDULIS. Shell bivalve. Valves ovate-roundish or 

 obovate. The upper one flat. Lamellce of both valves imbri- 

 cated and undulated. Vulva none. 



NATURAL HISTORY. 



The OYSTER, Ostrea edulis, is a well-known edible mollusk, 

 the shell of which is formed of two unequal valves connected 

 together by a hinge of the simplest character. Externally the 

 shell has a coarse and dirty appearance, each shell being com- 

 posed of a great number of laminaB irregularly closed down 

 on each other. In some species it is smooth, in others stri- 

 ated, tuberous, or prickly, the lower shell being always the 

 deepest. The animal itself is also of very simple structure. 

 No vestige of a foot can be seen, and the ligament which 

 unites the valves is of small size. On separating the valves, 

 four rows of gills, or what is called the beard) are observed at 

 a little distance from the fringed edge of the mantle. The 

 abductor muscle is situated at about the centre of the body, 

 near which the heart is to be distinguished, and the mouth 

 may be seen beneath a kind of hood formed by the union of 

 the two edges of the mantle near the hinge. Many curious 

 discussions have arisen as to whether oysters possess the 

 faculty of locomotion. It is well known that in general they 

 are firmly attached to stones or to each other, and it has been 

 stated and generally believed that they are not endowed with 

 any powers of changing their position. This much, indeed, is 

 certain, that it is one of the most inanimate of the Mollusca, 

 remaining fixed upon some submarine substance, enjoying 

 only the nourishment brought it by the waves, and giving 

 scarcely a sign of life, except the opening and shutting of its 

 valves. In the British Museum there is a large specimen of 

 a crab, to the back and claws of which a number of good- 

 sized oysters have attached themselves. From the observa- 

 tions and experiments of naturalists it appears, however, that 



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