1892.J The BRITISH NATURALIST. 



beaten from birch, and one from hazel. My friend, Mr. Chaney also 

 has taken the species this year. -Id. 



Pachyta collaris. -I found several specimens of this insect 

 during a recent visit to Farnham, Surrey. The species is said to 

 abound in hop grounds, its habitat being in the poles. Mine were 

 obtained, as usual, from Umbelliferse. — Id. 



MoHusca.— Notes. 



Notes on Varieties. — Mr. Taylor has published some extremely 

 valuable papers on "The Variation of the Mollusca" in a recent 

 volume of the Journal of Conchologv, from which I will quote those parts 

 dealing with the causes of variation, to which I shall add corroborative 

 facts and opinions deduced from them by other writers. I particularly 

 wish to call: attention to the following: "Environment is the most 

 powerful and perhaps the only force inducing variation, or rather 

 fostering those variations which are most in accordance with the 

 surrounding conditions . . . we are, however, often unable to 

 recognise the cause of many modifications, but it is patent that no 

 change occurs without a reason and no effect without a cause. VVe 

 must in those cases store away facts and observations to which we 

 may hope sooner or later to find the key." Supply of Lime : — 

 Deficiency of lime doubtless leads to the production of very thin, 

 fragile, and horny shells. A striking instance is seen in the 

 remarkably delicate form of H. aspersa, which is plentiful in some parts 

 of Guernsey. Clessin points out that the results of this deficiency are 

 also observable in the form of some shells, thus, he states that the 

 Claiisilice have their shells shorter than usual, and that H. lapicida 

 becomes somewhat rounded on the periphery. Peat moors, on 

 account of the absence of lime, produce dwarfed and fragile shells. 

 It is remarked that among fresh -water shells, some species, like U. 

 margaritiferus and Neritina, seem to have a superior power of with- 

 drawing lime from the water, producing solid shells in granitic 

 regions, while Ancihis, in the same water is said to be remarkable for 

 unusual thinness and delicacy. Dr. Jeffrys says, of the Pisidia, "Size, 

 substance, sculpture, and lustre . . . mainly depend on the 

 cliemical ingredients of the water inhabited by the molluscs, as well 

 as their supply of food." In 1885, I took a large quantity of Anodons 

 and Unios of extraordinary size from the bed of a lake from which 

 the water had been drained. On examination of the water after it 

 liad been aii'ain allowed to fill its former basin. 1 found it contained 

 16.2 grains of CaO per gallon, this is equal to nearly 2ej grains of 

 carbonate of lime, probably however, a considerable proportion 

 of this hme was in the form of sulphate, derived from the 



