PLATE XXVIII. 



are inequl valve and irregular, that they have a simple hollow for the 

 ligament as in the oysters, but that they are distinguished by a slope 

 at the side of the ligament for the passage of the byssus. 



It is assuredly true that the presence of a byssus in this tribe of 

 shells displaces them from any immediate analogy with the Ostrea^ 

 where as Cuvier remarks "Linnaeus left them/' But, if however, we 

 attentively examine the hinge of the common oyster, the two valves, 

 and the oyster as it hes within the valves, we shall perceive with this 

 exception a pretty near approximation. The great objection is, that 

 the animal of the tribe of shells now before us protrudes a byssus 

 from its body through a lateral opening on one side or slope of the 

 ligament of the hinge ; if we closely inspect the valves of the oyster, 

 we also find a slight depression or hollow upon each side of the carti- 

 lage of the hinge ; these are small, and usually somewhat lamellar. 

 The oyster, moreover, as it lies in the shell, seems capable of expand- 

 ing or spreading that part of the body which lies under the hinge 

 laterally upon and into these depressions, a circumstance very easily 

 observed in the half famished oyster, because these lateral expansions 

 of the animal are then more visibly elongated along the passage of 

 these lateral grooves of the hinge, and give the pointed end of the 

 animal a somevv^hat cornuted appearance. Under the same circum- 

 stance these processes adhere as they lie in the hollow of these grooves, 

 and thus suggests the idea of the animal having exerted itself by 

 such extension to obtain refreshment through these lateral hollows. 

 Those hollows are also so far pervious as to admit the ingress of 

 moisture while the shells are closed, in the same manner as it is 

 possible the Malleus genus may receive moisture under the same 

 circumstance through the sinus, whence the byssus is protruded. 

 These peculiarities considered, may perhaps afford some further 



