RIVALVKS OSTREA. ^^ 



©n <m^ side, which gives the outhne of the shell an ap- 

 pearance of slight distortion, oocosioncd by one margin 

 being straight and flattened, while the other remains 

 found and inflated. There is also considerable variation 

 in the size and form of the ears, which in some species 

 are nearly of the same dimensions, but in others are une- 

 qual, having one much larger than the other; and some 

 are so small as hardly to be discernible. 



The ears of many of the scallops are almost smooth on the 

 outside, whilst others have them rough, and even spined* 

 The Ostrea pallium, and others, have one ear ciliate, and 

 are spined within. The exterior of the shells, as has beea 

 before observed, is usually covered with elevated longitu- 

 dinal ribs and grooves, which are variously diversified 

 with beautiful colors and fine chequer-work. The ribs 

 are mostly covered with undulate and transverse striae, not 

 unfrequently assuming the appearance ofelevated scales, as 

 in the Ostrea imbricata and dubia. In others again the 

 strise are crenate, as in the Ostrea radula; and some, 

 as the Ostrea nodosa, &c. have large knobs or tubercle* 

 raised upon the ribs. The margins of the interior of the 

 Ostreae are mostly crenate or toothed, and are often beau- 

 tifully colored. 



The hinge is universally without teeth, and is furnished 

 with an ovate hollow; in the vicinity of which are 

 placed lateral transverse grooves, which run in a parallel 

 direction in each valve, but do not lock into each other, 

 as in the genus Area. This division of the Ostreae, viz. 

 the scallops, have the faculty of leaping out of the water, 

 even to the height of half-a-yard, or more; and, opening 

 their shells, they eject the water contained within them; 

 after which, sinking under water, they suddenly close 

 their shells with a loud snap. 



