35« 



Geographical Distribution of Mollusca. 



3. Large Lakes. 



Open Water. 



Litiinesa pereger Miill. 

 Plauorbis albiis L. 

 A)ioylns fluviatilis Miill. 



Example — Lake Windermere. 



Reed Belt. 

 Physa fontinalis L. 



Marsh. 



Siiccinen elegans Kisso 



Avion siibfusciis Drap. 

 Agriolimax IcBvis Miill. 

 Zonitoides nitidus Miill. 

 Euconuliis fulvus Miill. 



Ancylus fluviatilis occurs principally near the outflow, that 

 is in practically fluviatile waters. Avion suhfuscus is the domi- 

 nant species on the lake margin. Z. nitidus is typically a 

 non-calcareous marsh species, corresponding to the allied 

 species Z. excavatus on drier ground. 



In this section also comes : — 



Anodonta cygnea L., which is characteristic of a non-cal- 

 careous lake or pond with a muddy bottom. It is abundant 

 where it does occur, just as in the canal it takes entire possession 

 of the deeper water. No definite association of the habitat 

 can be given ; probably it is solitary. It is worthy of note that 

 the largest known specimens (measuring nine inches in length) 

 have been taken from a pond near Garstang. 



Sub-section 3a. — Soft Water Canals. (Example — Preston 

 and Kendal Canal). 



Reed Belt. 



Open Water. 



LimncBa pereger Miill. 



,, auvicularia L. 

 Planorbis alb us L. 

 Valvata piscinalis Miill. 

 Anodonta cygnea L. 

 Pisidiiim amnicum Miill. 

 SphcBvium lacustve Miill. 



On Rocks 

 Neritina fluviatilis L. 

 [Dreissensia polvniovpha 

 Pallas).* 



Marsh. 



L. tyuncatula Miill. 

 Pis. pusillum Gmelin. 

 Sticcinea piitris L. 



,, elegans Risso 

 Agriolimax agrestis L. 

 ,, IcBvis Miill. 



Arion atcr L. 



,, horie)isis Fer. 

 Vitrea crystallina Miill. 



,, radiatula Alder. 

 Z. nitidus Miill. 

 Eiic. fulvus Miill. 

 Hygromia granulata Aid. 



,, hispida L. 

 Cochlicopa lubrica Miill. 



As will be seen and as might be expected, the mollusc'an 



fauna places the canal intermediate between non-calcareous 



lakes and non-calcareous rivers. In the open water section 



there is a striking abundance of both Anodonta cygnea and 



Neritina fluviatilis, the former a species pre\-ailing in the deeper 



non-calcareous ponds, and the latter typical of slow-flowing 



* An introduced alien. 



Acroloxus lacustris 1^. 

 Limncsa palustris Miill. 

 Planorbis umbilicatus 



Miill. 

 ,, vortex L. 



,, fontanits 



Lightfoot. 

 Physa fontinalis Drap. 

 Bithynia tentaculata L. 

 Valvata cristata Miill. 

 SphcBrium corneuni L. 

 Pisidiurn fontinale Drap. 

 milium Held. 



Naturalist 



