No. 473] 



MUTATION IN MOLLUSC A 



333 



'The pond : 



hundred feet above the bed of Farmingto 



Tryon says: "Besides the above two species I found a single 

 specimen of Lymnoea umbrosa Say, and several of L. desidiosa 

 Say." 



From the foregoing account it would appear that shurtlejji 

 (Fig. 4) was an offshoot (or mutant, if we apply the de Vries 

 theory) of umbrosa^ {= elodes = palustris), that being the only 

 other species present (save desidiosa, which belongs to quite 

 another group of Lymnseas). It may be thought by some that 

 shurtleffi might have been produced by un- 

 favorable conditions, but as the shells, one 

 of the original lot of which was recently 

 examined by the writer, are perfect and not 

 distorted, this could hardly have been the 

 case. All the evidence points to the con- 

 clusion that shurtleffi is a new species evolved 

 or given off from palustris. The short, acute 

 spire, subcylindrical, compressed body whorl, 

 the partly open umbilicus, and the long and 

 narrow aperture are the principal character- 

 istics of the new species. 



The foregoing remarks are not made with ^'^riir coiype" 



the idea of fastening the mutation theory From Weat(.Ku.'. con- 

 upon the Mollusca, but only to call attention 



to these apparently analogous cases of mutation and variation 

 to the end that other zoologists may take up the matter and by 

 experimentation and by the study of abundant material from 

 various localities gather a large amount of data bearing upon 

 this theory as applied to the Mollusca. 



While the mutation theory seems to fit in very nicely in explain- 

 ing the very large amount of variation in the fresh-water pulmon- 

 ates, we must not be too hasty in applying this new theoiy, founded 

 as it is upon plant variation, to animal life. Dr. J. A. Allen, in a 



'Umbrosa is placed by some conchologists in the synonj-my of reflexa. I 

 have examined the type specimens in the Philadelphia Academy and they 

 are good examples of elodes. 



