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 

 Myae 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 alto- 

 gether destitute of teeth ; these have a rounded 

 cavity for the reception of the cartilage. The 

 gaping of the valves is another distinguishing fea- 

 ture, but it does not always occur. In form 

 also the shells differ considerably ; some are 

 oblong and truncated, 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 Myae 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; others are remarkable for 



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

 to lie open. 



*h Callosity, hardness of skin or flesh, from Latin call its, 

 which has the same signification ; hence our English word 

 callous. 



