66 BIVALVE SHELLS. 



curves which the hoof-like body assumes, which fit it 

 for lying on loose sand, without becoming deeply buried 

 in it. It is difficult to make this peculiar form clearly 

 understood by mere description, but I have said suffi- 

 cient to identify the object. 



The Mollusca which inhabit sandy shores habitually, 

 and in the greatest numbers, are not the Univalve, or 

 snail-like families, whose organization is more adapted 

 for crawling over rocks and sea-plants, where also they 

 find their appropriate food ; but another very distinct 

 group of shell-coated animals, called CONCHIFEEA,* or 

 TESTACEOUS ACEPHALA, which are capable of living 

 buried, sometimes to a considerable depth in the sands. 

 Some of this class of animals are indeed confined to 

 rocky places, anchoring themselves in various ways per- 

 manently in a position, either on a rock or on the stem 

 of a sea-weed ; or forming hollow chambers by burrow- 

 ing in the solid rock itself; but the majority of species 

 inhabit sandy places, and their shells continually meet 

 us on the sandy shore, while the living animals may be 

 detected buried along the margin of the retreating tide. 

 The shell, in all these animals, consists of two principal, 

 saucer-shaped pieces, more or less perfectly covering the 

 body of the animal, and united together by a more or 

 less complex hinge, opened by a highly-elastic ligament. 

 The Scallop and the Common Cockle offer well-known 

 examples of such a shell : the first having a simpler 

 structure, both in the hinge and in the animal, is better 

 adapted for explaining the general features of organi- 



* " General Outlines of the Animal Kingdom," by Professor Rymer 

 Jones, p. 375, et seq. 



