animals are quite amphibious, some of them living on the roots and 

 leaves of the vegetation which overhangs the water. A small British 

 species, Neritinafluviatilis, lives in the rivers of England, but the great 

 majority of species live in salt or brackish water. 



The family Centkiidce comprises some very handsome shells which 

 inhabit salt, brackish, or fresh water. They are found throughout the 

 world, but the finest species live in the tropics. The spire is very 

 long, and is composed of many whorls. Some shells are smooth and 

 polished, while others are marked by frills, knobs, spines, and ribs. The 

 name Cerithium is from the Greek, ceration, meaning a small horn, and 

 is given because of the horn-like shape of the shell. This family has its 

 giants and also its pigmies. The latter are pretty, reticulated shells, from 

 one-fourth to three-fourths of an inch in length, which live among the 

 eel-grasses and other vegetation along the shore. There are over one 

 hundred species of these small shells, some with dextral and others with 

 sinistral apertures. When handled, some of these mollusks discharge 

 a bright green fluid. 



The Potamides, comprising the fresh and brackish water Ceritkites, 

 generally have blackish shells without color markings, and inhabit 

 streams, swamps, and salt marshes. Some of the species are able 

 to suspend themselves from bushes by means of glutinous threads. 

 In many of the islands of the Indian and Pacific oceans the animal 

 is roasted and eaten by the natives, who suck the contents through 

 a hole in the spire. 



Whoever visits the seashore is bound to become intimately 

 acquainted with the Littorinas or periwinkles, for they cover the rocky 

 shores everywhere, millions of their rounded shells clinging to the rocks 

 when the tide goes out. They live principally in the littoral region, 

 feeding on the algoe which grows near the shore. They are also found 

 both in brackish and in fresh water. The common periwinkle, Littorina 

 littorea, is extremely abundant on the shores of southern Europe and 

 in the northern part of the United States. In England it is used 

 as an article of food, and it is said that nearly two thousand tons are 

 gathered annually, and a thousand persons are employed in their 

 capture. In London and in other large cities they are sold on the 

 streets in the same manner that we sell peanuts, and the animal 

 is picked out with a pin. It is used for bait in some of the fisheries, and 

 the oystermen annually plant many bushels on their oyster beds to keep 

 the seaweeds from accumulating. From these facts it will be seen that 

 this periwinkle is of considerable economic importance. This species 

 is also remarkable for the length of its radula, which is coiled in the 



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