1892.] 



THE BRITISH NATURALIST. 



15 



Mollusca. 



A FEW NOTES ON FRESH-WATER SHELLS. 



BY W. A. GAIN. 



Some months ago I saw the opinion expressed that the var. labiosa 

 of Limnoea peregra was produced by the animal, during shell-growth, 

 crawling over a hard surface, mud which had hardened during a 

 previous drought and afterwards been overflowed on the filling of the 

 ponds by succeeding rain. 1 cannot find the article, so am unable to 

 refer the reader to it, or to give the name of the writer, but last year 

 some facts came under my notice which tend to confirm this opinion. 

 I must first state that what I term my aquarium is not quite in the 

 ordinary style, it consists of a stone trough, containing about 130 

 gallons, placed in a shaded part of the yard, and about two-thirds 

 covered by a massive flag-stone ; it is never cleaned out, and contains 

 a varied assortment of animal and vegetable life, in fact I have 

 endeavoured to produce as nearly as possible the conditions found in 

 a natural pond. In this aquarium nearly half the number of full- 

 grown specimens of both L. peregra and L. stagnalis were found to 

 have expanded and refracted lips, attributable, I believe, to the hard 

 sides of the trough which they delight to ascend, and browze on the 

 plentiful herbage to be found there. 



On one occasion, while watching an example of L. peregra floating 

 shell downwards on the surface, with the foot very concave, I saw the 

 animal extend its tongue and seize a minute portion of what looked 

 like bread crumb, which floated just in the centre of the concavity, 

 and convey it to his mouth. 



Varieties. — Are we not sufl'ering from a plethora of varietal 

 names ? By the naming of slight variations from the normal forms, 

 many of which are so close that in a number of cases it is impossible 

 to say to which var. a certain shell belongs, we are getting the 

 nomenclature of our land and fresh-water moUusks complicated 

 enough to puzzle a Philadelphia lawyer. A systematic weeding of 

 our too abundant varietal names is a thing to be desired. Those 

 names indicating well-marked variations from the type should be 

 retained, as the use of them affords the readiest and most exact means 

 of describing a shell. One of the worst of recent innovations is the 

 introduction of names from continental sources for the different band 

 arrangements. These are quite unnecessary as the old band formula' 

 convey the information much more clearly and exactly. Again, what- 

 good can be served by such terms as fuliginosa applied to a shell 



