SHELLS. 35 



Child. Yes, it is marked by a rib like that 

 at the opening. 



Teacher. You will find a great many shells 

 which shew that they have been enlarged in the 

 same manner. The fresh layers are parallel to 

 the margin of this opening called the mouth, 

 and the meeting of the edges of the new and 

 old matter is often marked by a ridge more or 

 less elevated, 



The shell of the adult animal is often armed 

 with inequalities on the surfaces, as spines or 

 tubercles, which do not appear in the young 

 shell. I will now give you a summary of the 

 lesson of to-day, 



SUMMARY. 



The mo 11 use a are often placed in situations 

 of great danger. They are exposed to the 

 dashing of the waves, often borne by th vio- 

 lence of storms and cast against rocks or stones. 

 Some placed in rapid rivers are occasionally 

 hurried along by the impetuosity of the stream, 

 God, however, always makes a suitable provi- 

 sion for the circumstances under which he places 

 his creatures, and when he apportions to them 

 spots of danger, arms them with the means of 

 protection and defence. Thus we find that the 

 shell and the habits of the mollusca are adapted 

 to the situations which they occupy. Some that 

 belong to the rapid rivers of America have an 

 exceedingly hard and substantial shell, fitted to 

 contend with the most boisterous elements ; 

 D2 



