10 WEST COAST SHELLS 



these naked mollusks slugs, and most people have 

 very little love for them, for they have greedy appe- 

 tites and can destroy young pansies or lettuce plants 

 in a single night. During the daytime they com- 

 monly keep out of sight, getting into cracks in the 

 ground or under old boards, where they may be found 

 and destroA'Cd. The chief kinds that live in this 

 region will be described on a later page. There are 

 some naked slugs in the sea too, but most of the 

 marine mollusks are provided with strong shells, and 

 it is the purpose of this book to describe them. 



We understand that the first object of these shells 

 is the protection of the creatures that carry them 

 around, and it is exceedingly interesting to see how 

 well they are adapted to this purpose. But as we 

 wear clothes that are supposed to be somewhat orna- 

 mental as well as useful, and as we paint and deco- 

 rate our houses, so many mollusks build very gor- 

 geous coverings for their bodies, though it is true 

 that much of the beauty does not appear until after 

 the death of the humble builder. Of course we know 

 very little about the motives which impel these crea- 

 tures to construct their shells, and we can only fall 

 back on that old word ''instinct," which has received 

 so many different explanations. Perhaps we cannot 

 do better than to call it the guiding influence of the 

 great Creative Power that controls all nature. 



The material of which shells are made is carbonate 

 of lime, the basis of all limestone, chalk and marble. 

 This substance is very widely distributed, though 

 in some soils and some rivers it is far more abundant 

 than in others. For this reason land and river shells 



