No. 435 ] SHELL OF UTTORINA UTOREA. 183 



This is, nevertheless, so great that we are reluctantly forced 

 to the conclusion that Littorina /itoirn, which on account of its 

 comparatively recent migration to our shores, and its great 

 abundance and variability seemed an especial!}- favorable object 

 for statistical study, is after all not suitable for this purpose. 

 In order to use this material we must either assume that the 

 causes of erosion have a uniform intensity for all individual-, or 

 else we must devise some easy method for determining the actual 

 loss of substance 111 each individual. But even these precautions 

 would not enable one to use this material for the solution of the 

 special problem that we had in view. 



