INTRODUCTION. IX. 



Valvata piscinalis, Achatina acicula, Pupa Venetzii. 

 The species found in the older series differ from the 

 recent British Land and Fresh-water Mollusks in being 

 considerably larger, and are more nearly allied to our 

 present tropical species. Had our limits allowed of it, 

 we should have somewhat enlarged our observations 

 on Geological distribution, a branch which has hitherto 

 been overlooked. It would be advisable for readers 

 in different parts of the country, to record in some 

 of our Natural History publications, not only lists of 

 shells found in the district in which they live, but also 

 the circumstances under which they are found, the 

 formation of the rock, or the nature of the water, &c. 

 We append a few of the many works that can be 

 consulted, by those who are desirous of further in- 

 formation respecting the structure, organization, &c. 

 of these little creatures, than the object of the present 

 work will allow. At the same time we would advise 

 our younger readers to make their own observations 

 and compare them with those of others, rather than 

 learn from works of art what can only be properly 

 acquired by an inspection of nature herself. What 

 could afford more delight than to make the Fresh- 

 water varieties the inmates of vivariums, where their 

 peculiarities could be watched day by day, or to colo- 

 nize our neighbouring woods and hedgerows with some 

 of the land species ! 



In the wonderful structure and development, as well 

 as the habits of mollusks, there are many peculiarities 

 that are common to all, so that to the reflecting student 

 a thorough investigation of a few of the commoner 

 species, may furnish him with a vast amount of in- 

 formation. 



