34 INTRODUCTION. 



confined, as far as I have had the opportunity of 

 learning, to the southern part of the island. Mon- 

 tagu says that Dorsetshire is the western limit of 

 the Neritina ; this is curious, as it and the two species 

 of Paludina are found in Ireland. 



Segmentina lineala has only been mentioned as 

 found near London and in the south-west of Eng- 

 land. Near London it is not uncommon. 



LimncBus acutus (if it is more than a variety of 

 L.pereger] has only been recorded as found in South 

 Wales. 



Cyclas rivicola is almost peculiar to the Thames : 

 its northern limit is, I believe, the Trent in Not- 

 tinghamshire : it is also found in Germany. 



Pisidium obtusale^ P. nitidum, and P. Henslow- 

 ianum, have only been recorded as found near London, 

 in Surrey, and in Cambridgeshire ; but this, perhaps, 

 is because they have not been searched for elsewhere. 



The Uniones ( U. pictorum, U. tumidus, and U. 

 Batavus) are not recorded as being found in the north 

 of England, or in Scotland, as far as I know. 



Among the southern terrestrial species, Testacella 

 haliotoidea seems confined to the gardens in the neigh- 

 bourhood of London, Plymouth, Biddeford, and to 

 the island of Guernsey. 



Helix obvoluta, to the chalk downs of Hampshire. 

 This species is common to the north of France and 

 Germany. 



Helix limbata has only been found in the hedges 

 near Hampstead, Middlesex ; but it is very doubtful 

 if these specimens had not been introduced: it is 

 common in the southern part of France, and has 

 been found as far north as Caen. 



