46 Dzvellers of the Sea and Shore 



confused. Let me, therefore, hasten to set him right. 

 It will be easy to do this by summarizing. 



The MoUiisea are divided into five classes. These 

 classes, taken in the order of their supposed relation- 

 ship, are respectively the Amphineiira, Gastropoda, 

 Scaphopoda, Pelecypoda, and the Cephalopoda. With 

 the exception of the Amphineura, a group that includes 

 the curious chitons and their allies, the modification of 

 the foot is the basis on which these classes have re- 

 ceived their various names. For it will be noticed that 

 the terminations of the remaining four names refer to 

 the foot. Thus, the Gastropoda, represented by the 

 common garden snail, the moon snail, the periwinkles, 

 and other mollusks bearing but one shell, usually 

 spirally coiled, crawl on the thickened under surface of 

 their bodies. That is to say, the foot. The Scapho- 

 poda, whose shells are like little elephant tusks open at 

 both ends, burrow in the sand or mud with a long 

 wormlike foot. The Pelecypoda, to which belong the 

 familiar oyster, clam, and mussel — bivalves all — are 

 variously endowed in respect to the shape of foot, but 

 the prevailing type is club- or hatchet-shaped. The 

 Cephalopoda are distinguished among molluscs by 

 having the foot modified into a number of so-called 

 "arms" which encircle the head or the mouth. It is 

 to this group that the squid, the octopus, and the pearly- 

 shelled, chambered nautilus belong. 



It is the class Gastropoda, however, that is the 

 largest and most comprehensive of the five subdivisions. 

 It far outnumbers the others, both in species and indi- 

 viduals. Moreover, it is among these that are found 

 the only members of the entire group of mollusks which 



