INTRODUCTION. XXXI 



Land shells are to be found in different situations ; 

 some prefer dry banks, and exposed heaths, while 

 others live in moist places, near running water, in 

 thick woods, or in the crevices of old walls. The 

 smaller species are frequently found sheltered under 

 the moss which grows at the foot of trees, and 

 sometimes in the decayed wood. In the spring, 

 they often retire from the heat, under great stones. 

 In winter they must be looked for in holes of trees, 

 in the slits of the bark, or in the fissures of rocks. 

 But, in general, the most favourable time for the 

 discovery of these animals is the spring ; because, 

 in that season, they rouse from the torpidity of 

 winter, and go forth Avith fresh vigour to seek for 

 food. 



The fresh- water shells are far less numerous than 

 those which inhabit the land. They are found not 

 only in rivers, and springs, but also in ponds and 

 marshes, and even in muddy ditches. Some bury 

 themselves to a certain depth in the sand, or the 

 mud ; while others live attached to stones at the 

 bottom of the stream, except at times, when they 

 leave the water to climb up the plants which grow 

 upon its banks. The smaller species are the most 

 difficult to procure, as, from their diminutive size, 

 they readily escape observation. The best time to 

 look for fresh- water shells, is from the end of spring 

 to the middle of summer. At other seasons, they are 

 thrown dead upon the banks, and often mixed with 



