INTRODUCTION. O 



place, and should any stranger wish for further informa- 

 tion than can be obtained through the glass cases, the 

 curator will always be ready to give courteous attention to 

 his enquiries. 



Though the entire list of British land and freshwater 

 species is limited to 130, there are numerous varieties of 

 most of these ; so that while a fair collection is within the 

 reach of most people often within the range of a single 

 county a perfect collection takes a long time to accu- 

 mulate. 



The pleasures of collecting anything are too patent to 

 need to be dwelt on here, but the pleasures of collecting 

 objects of natural history in any branch have additional 

 charms the charms of the country. 



It should not be supposed that the summer is the only 

 time when it is possible to collect. Throughout the winter 

 much may be done, except, of course, when a frost puts an 

 end to turning over stones, and drives all water shells into 

 the mud. 



Doubtless every describer of shells has been puzzled to 

 find simple geometrical terms suitable to their forms, which 

 are often complex. I have followed the authorities in 

 using such terms as ovate, sub cylindrical, &c., though they 

 are vague, and do not express to what degree the object is 

 oval or cylindrical. Dr. Jeffreys calls L. stagnalis " elon- 

 gated," which it certainly is ; but what shape is " elon- 

 ated " ? This difficulty, however, affects the describer 



