BRITISH 



LAND AND FRESHWATER 

 MOLLUSKS. 



The inland molluscan fauna of the British. Isles is very limited in 

 kind, compared with that of more southern European countries, or 

 with that of America within the same isothermal latitude as Britain. 

 The warmer temperate districts of Europe, marked by the olive, and 

 even the vine, show a material increase in the development of mol- 

 luscan life; while in the intertropical region of the palms, embra- 

 cing all that is most productive in the conditions of light, heat, and 

 vegetation, its abundance is prodigious. Upwards of seven thou- 

 sand land and freshwater shells have been described from all parts 

 of the world, of which scarcely more than a hundred and twenty 

 are British. To the casual observer, a few slugs and snails in the 

 garden or on the chalk down, a few water-snails and little horny 

 bivalves in our ponds and ditches, and a pearl-mussel or two in 

 our running streams, are all that present themselves to his attention. 

 The remainder are minute forms, Hving more or less concealed 

 in moss, or among the decaying roots of shrubs and bushes, only 

 to be procured with dibgent search at the proper times and 

 seasons. Our molluscan fauna, too, is simply European in its cha- 

 racter; it possesses no local typical speciality like the fauna of 

 Madeira or of the Sandwich Islands. Our groves do not glow be- 

 neath the same tropical sun as the woods and forests of the Philip- 

 pine Islands, of Bolivia, or of Venezuela; and our running streams 

 are small indeed compared with the mighty rivers of America. 

 But although our land and freshwater moUusks are small, and singu- 

 larly limited in kind, they present equally interesting features for 

 comparison and study. With these few introductory remarks, we 

 pass to our tabular exposition of the classification. 



B 



