150 NELSON : ON PLANORBIS CORNEUS. 



will also furnish a useful bibliographical guide to malacologists 

 generally. The labour of compilation must have been enormous, 

 otherwise one would be tempted to wish that the index had been 

 much fuller. As it is, though there is a double reference to the 

 author's names and to the names of the molluscs, there is no 

 reference to the titles of articles. With regard to the index of 

 molluscs it seems to us that MM. Crosse and Fischer would have 

 adopted a much better principle if they had given the references 

 to the specific instead of to the generic names. 



A VARIATION IN THE COLOR OF THE ANIMAL 

 OF PLANORBIS CORNEUS, 



By WILLIAM NELSON. 



During the summer of 1878 I visited a small cattle pond 

 situated near to Temple View, York Road, Leeds. At one end of 

 the pond is a dense growth of reeds, Elodea canadensis, Callitnche 

 verna and Lemna minor, and several freshwater algse; while the 

 other end of the pond is shallow and quite destitute of plant life. 



Dredging among the plants I obtained specimens of a dwarf 

 form of Sphce.niim lacustre, also Pisidium pusiilum and Planorbis 

 naittileus very plentifully. On proceeding to search the shallow end 

 of the pond I was surprised to see a number of Planorbis corneus, 

 many of them having the animal of a bright flesh or pink color, 

 the animals being mostly protruding from the shell and very con- 

 spicuous. This somewhat remarkable divergence from the normal 

 coloration of the animal was shared to some extent by the shell, 

 which was much thinner, more diaphanous than the type, and 

 suffused with a sHght tinge of pink. Intermediate gradations of 

 color connected this singular variation with the normal form. 

 The phenomenon would appear merely to have been temporary, 

 as it was in vain this spring that I again searched the pond, not 

 being able to discover a single example of the species. 



J.C, ii., May, 1879 



