6 JONES : MOLLUSCAN ALBINISM. 
tain combination of iron. It may be urged that a similar 
explanation will suffice for those parti-coloured individuals 
which have been captured at large. I do not think it will, 
and for this reason: if the cause had been one dependent on 
food material, all the animals in a certain locality would have 
presented pseudo-albino tendencies, as was the case with Capt. 
Farrer’s Helices, but this, so far as we know, has not been 
noticed with regard to free-roaming snails. Such an explana- 
tion will in no case account for the abnormality in the specimens 
of Planorbis corneus mentioned above, which were taken where 
both the white variety and the type existed under exactly 
similar conditions, and living on the same kind of food in the 
same pond. 
Albinos, as a rule, are taken under one of two conditions: 
either singly or in colonies. Many instances, embracing many 
species, both freshwater and terrestrial, can be cited in proof of 
this. There is a pond at Birch in which occurs /lanorbis 
corneus var. albida in such quantities that last year the white 
specimens numbered 73 per cent. of the whole! Again, ina 
pond at Gorton, I found white Planorbis corneus present to the 
extent of 16 per cent. 
Among the terrestrial mollusca, the tendency to form 
colonies is still more marked. Capt. Farrer communicates to 
me that he has found Clausilia rugosa var. albida congregating 
in quantities on a wall near Kew Gardens. ‘The same observer 
finds that although Helzx rotundata can be found in any quantity 
around Bassenthwaite, there is only one spot-—a certain heap of 
stones—where the white variety occurs, and that in that spot 
the type is never met with. The white variety is so numerous, 
however, where it occurs, that he has taken as many as fifteen 
specimens from the same stone. Last year, Mr. F. Taylor, 
a member of the Manchester Branch, took at Plumstead, 
Flyalinia nitidula var. helmit and H. rotundata var. alba, 
both living in large colonies and within circumscribed limits. 
Mr. Charles Oldham informs me that some years ago he took 
J.C., viii., Jan. 1895. 
