FRESH- WATER LIMPETS. 57 



observed, sportively as it were, picking off these tiny 

 molluscs from the weeds in our streams and mill- 

 ponds, we believe that the staple article of food with 

 all the Grebe family is fish. 



Although a few other aquatic species may be 

 discovered by the industrious conchologist, we believe 

 we have now mentioned all that are most likely to 

 be met with by collectors in the environs of London. 



There are still a few terrestrial mollusca which, 

 unlike those already named, are unable to endure the 

 smoky atmosphere of town and suburbs, and must 

 accordingly be sought for in the purer air and more 

 congenial haunts of wood and field. Some, as Helix 

 virgata, caperata, cartusiana, and ericetorum, al- 

 though deserving of a place in a list of shells found 

 in the environs of London, are nevertheless peculiar 

 to the chalk, and not to the London clay, so that it 

 may be convenient perhaps to defer noticing them 

 for the present, until we have concluded our remarks 

 on those which are not restricted to a chalky soil, 

 and which may therefore be met with much nearer 

 to the metropolis. Moreover, by bearing in mind this 

 distinction of habitat, the memory will be assisted in 

 discriminating many allied but distinct species. 



