242 COMMON FRESHWATER SHELLS. 



great deal. For even if his scientific research is of so high an 

 order that he knows a rook from a starling and a blackbird from a 

 bullfinch, that he has ceased to regard a bat as a bird, and a whale 

 as a fish, he still probably classes land-snails as insects and sea- 

 snails (best known to him in the form of oysters, cockles, whelks, 

 etc.) as fishes. Many people — perhaps most people — do not know 

 that there are such things as Freshwater shells, and as these are so 

 easily to be found, and some species are so very abundant, this is 

 rather to be wondered at. 



The great abundance of any one species admits of one par- 

 ticularly interesting study — namely, the noting of the different 

 varieties to which that species is subject. If, for example, there 

 is an abundance of food, we get fine, large shells ; if, on the other 

 hand, food is scarce, we get stunted shells. Heat, again, in one 

 species at any rate, produces thin shells ; absence of lime gives us 

 decollated shells. This is very well illustrated by that extremely 

 common freshwater shell, Limncea peregra. Some shells of this 

 species are small, very delicate, and almost without colour, whilst 

 others are thick, heavy, large, and dark ; some are very broad, 

 others very narrow ; some glossy and others dull ; and one variety, 

 known as ''burnetii,'' has no spire. 



This is a gregarious species, the animals being found together 

 in very large numbers, and as the animal is extremely prolific this 

 is to be expected. It inhabits rivers, streams, ditches, ponds, and 

 lakes, and is found in every part of Great Britain. It is an active 

 animal, often leaving the water to climb upon the stems and leaves 

 of surrounding plants or crawl about on the mud, thus earning its 

 specific name — peregra, " wandering." It frequently wanders 

 to some distance from its usual home, and when in cap- 

 tivity is given to leaving the vessel in which it is supposed 

 to be confined. Although, as a rule, it is a vegetable feeder, 

 it has been known to attack and kill fish when kept in the same 

 aquarium, and also to eat the dead bodies of members of its own 

 species. It has even been known, when pressed by hunger, to 

 attack and eat its own fellows. On the other hand, it is the prey 

 of birds and fishes ; also leaches, and parasites known as Gordias. 

 A distinguished conchological member of this Society* says 



*The Leeds' Naturalists' Club and Scientific Association. 



