CHAPTEK VIII. 

 THE CLAM AND OTHER BIVALVED SHELL-FISH. 



Iisr walking along the sea-shore, the commonest shells one 

 picks up are the long clam, the round clam or quohog, the 

 mussel, and perhaps scallop- and oyster-shells ; and if one 

 lives inland and walks by the river-bank, one is apt to meet 

 with pretty mussel-shells, brown outside and of a deep 

 pearly purple within. The sea shell-fish can be also bought 

 fresh in the market ; and we will suppose that we are ad- 

 dressing a class of boys and girls, sitting around the table, 

 each with a shell in his or her hand. We will begin with 

 empty clam-shells. Now, what shall we observe ? Look 

 first at the two shells, which may be held with the two 

 sides or valves closed. Each shell is called a valve, and as 

 the soft animal or clam is protected from harm by two 

 solid valves of lime, it is called a bivalve. The two valves 

 are alike, whether seen from without, from above, or below, 

 of 1 from either end. If, however, we look at the whole 

 shell from the side, we see that the two ends are unlike, 

 that it is somewhat wedge-shaped, one end being less 

 rounded than the other. As the head of the animal lies in 

 the rounder end, this is called the anterior or front end. 

 When the clam burrows in the mud, the anterior end sinks 

 down first. The sharper end is called the posterior end : 

 it is this end which remains uppermost in the clam's hole. 



If we now open the two valves and look at their inner 

 sides we shall see that they are unlike. One of them has a 

 large projection on the edge ; this is called the "tooth," in 

 the other shell there is a cavity corresponding to the tooth. 

 This cavity and the hollow on the inner side of the large 

 tooth isj if the shell is a fresh one, filled with a dark-brown 



