COMMUNICATION 
TO THE 
MONTHLY MEETING 
OF THE 
YOEKSHIRE PHILOSOPHICAL SOCIETY, 
1883. 
December 4tb, 1883.—Tbe Pev. W. C. Hey, M.A., read 
the following paper on “ Tbe Eorms of Pond-snails in Yorkshire.” 
In a previous paper read before this Society, I described some 
forms and varieties of Land-snails, suggesting some possible 
explanations of these varieties, and also pointing out the diffi¬ 
culties on which these explanations throw little or no light. 
Our Pond-snails also present considerable variety—not so much 
variety of colouring as the Land-snails, but a far greater 
variety of form. 
Almost all air-breathing Pond-snails are of an uniform 
horn colour. One might be tempted to explain this lack of 
brilliant colouring so conspicuous in Land-snails, on the ground 
that in their weedy, watery element they were less accessible to 
the rays of light; but the fact that sea-shells living in far 
deeper waters are often most gorgeously tinted, rather militates 
against such an hypothesis. Perhaps we must rather look to 
that “ Deus ex machina ” of the modern scientist—natural 
selection—and believe that the colouring of Pond-snails is 
protective, as it renders them very inconspicuous among the 
watery weeds. 
In the genus Limneea (to which the following remarks 
exclusively refer) only two variations from the normal colour 
occur, at any rate in Britain. White varieties are knovui of 
several species, e.g., L. glabra occurs in a white form at York, 
