150 BIVALVES. 



inequilateral., mostly gaping at both ends, gene- 

 rally smooth, or only slightly striated ; shape 

 suboval, broader than it is long ; hinge with a 

 strong, patulous,* or spoon-shaped tooth, some- 

 times inserted into the opposite valve. 



OBSERVATIONS ON THE SHELL AND ITS 

 INHABITANT. 



The points of generic resemblance in the Myee 

 are wanting in many of the species. The coarse 

 large tooth is the characteristic of the hinge, but 

 sometimes it is not more than a thickened 

 callosity. f Some species are altogether destitute 

 of teeth ; these have a rounded cavity for the re- 

 ception of the cartilage. The gaping of the 

 valves is another distinguishing feature, but it 

 does not always occur. In form also the shells 

 differ considerably ; some are oblong and trun- 

 cated, as if a part of the shell had been cut off ; 

 others are orbicular, and many are angular from 

 the addition of ears at the hinge. The Myse are 

 generally covered with a thick brown or green 

 epidermis ; when this is removed, the surface 

 exhibits a beautiful iridescent mother-of-pearl 

 lustre. Some of the species grow to a great size ; 



* Patulous, lying open, spreading, from the Latin pat ere 

 to lie open. 



j* Callosity, hardness of skin or flesh, from Latin call s, 

 which has the same signification ; hence our English word 

 callous. 



