NOTES AND QUERIES. 285 
MOLLUSCA. 
Limnza involuta probably a Variety of L. peregra.—The question 
broached by Mr. More (pp. 154 and 155 ante), as to what is now known 
as L. involuta being merely a variety of L. peregra, I may point out, is not 
new. Adams, on p. 35 of his ‘ Collector’s Manual of British Shells’ (1884), 
broaches the question, but, without giving any reasons, siraply remarks, 
“Tt is probably a variety of Limnea peregra.” I would like to ask 
Mr. More on what physiological or other grounds is it conceivable that 
the scanty supply of lime-salts and of food-stuff in the Lough could produce 
an involuted spire? If the smallness of the mountain tarn and the isolation 
of involuta have anything to do with its conversion into that form from 
L. peregra, then I would point out that there seems to me here a con- 
tradiction. I presume that for the sake of the exactness of experiment 
Mr. Waller kept the involuta Mr. More sent him isolated, and also I presume 
the tank—or whatever he used—was somewhat smaller in its capacity than 
Lough Crincaum. Then, taking the supposition that these two conditions 
obtained in Mr. Waller’s experiment, and taking also the supposition that 
the isolation and the smallness of the mountain tarn may have produced, 
or have helped to produce, the conversion of L. peregra into L. involuta, 
we have the anomaly of similar causes producing two diametrically opposite 
effects—in one case the conversion of L. peregra into L. involuta, in the 
other the reversion of L. involuta into L. peregra. In this, I consider, lies 
the futility of the evidence advanced by Mr. More in favour of the theory 
he promulgates. Again, supposing that the scarcity of lime-salts and of 
food-stuffs in the Lough may have produced, or have helped to produce, 
the conversion of L. peregra into L. involuta, I may point out that there 
exists a thin and small variety of L. stagnalis (called var. fragilis by 
Jeffreys) which may be as legitimately considered to be produced by the 
scarcity of lime-salts and of food-stuffs in the medium in which it lives, yet 
it does not possess an involuted spire. Against this supposition, however, 
I would point out a statement for which Prof. Rolleston and Mr. W. 
Hatchett Jackson (‘ Forms of Animal Life,’ 1888, p. 127) are answerable :— 
“The thickness of a shell does not depend upon the amount of lime in the 
waters in which the animal dwells, but rather on the workings of its tissues, 
modified by surrounding influences, whether chemical or non-chemical. 
This may be readily seen by a comparison of the dense shell of a Pearl 
Mussel, Unio margaritifer, from the mountain-streams of Westmoreland, 
with the thin shell of Anodonta from Oxford waters, much richer in lime.” 
And even if here these authors are speaking specially of the Lamellibranch 
shell, yet there is no reason why it should not equally apply to the shell 
of a Basommatophor. The very fact that Mr. Waller fed his involuta upon 
water-cress lends a decided assumption to a belief that he accidentally 
