ANOMIA ANTIQUE LAMP. 185 



OBSERVATIONS ON THE SHELL AND ITS 

 * INHABITANT. 



This genus contains a variety of shells mate- 

 rially differing in their appearance. The perfor- 

 ation in one of the valves for the emission of a 

 ligament, by which the animal adheres to marine 

 substances, is, perhaps, the most general, though 

 not an invariable characteristic. 



The Anomiae are now arranged in two prin- 

 cipal groups, very clearly distinguished from 

 each other. The shells of one division retain the 

 name of Anomia, and very much resemble a 

 small oyster in their appearance ; like them they 

 are fixed and stationary, living and perishing on 

 the spot where the egg was first deposited. 

 They are attached by means of a bony appen- 

 dage, having a dilated base ; this is in fact only 

 a prolongation of the adductor muscle of the 

 animal ossified at its outer extremity. When 

 the mollusk contracts the muscle, the dilated 

 portion is drawn over the perforation of the 

 flattened valve and covlrs it, acting as an oper- 

 culum. So firmly are the shells fixed by this 

 organ, that they cannot be removed from their 

 retreat, without destructive violence, the liga- 

 ment and operculum being left on the rock to 

 which they were cemented. The form of the 

 Anomia, like that of all stationary shells, is very 

 irregular, being usually modified by the sub- 

 stances to which it adheres. The prevailing co- 



