SOME INTERESTING MOLLUSCAN MONSTROSI- 

 TIES.* 



Frank Collins Baker. 



The study of abnormal and pathologic specimens of the 

 Mollusca is of great importance in assisting us to understand 

 the biological causes for the specific variation of our fresh 

 water shells. Monstrosities among land and fresh water 

 shells are constantly occurring and are, curiously enough, more 

 often produced by external causes, as man or cattle, than by 

 the atrophy or hypertrophy of any part of the animal. 



Fords and shallow bars of rivers and lakes are the best 

 localities in which to find abnormal individuals, as in these 

 places cattle and horses are passing to and fro and injuring 

 the shells with their feet. 



Several years ago Mr. Charles E. Beecher, in a paper on 

 Abnormal Fresh- water Shells,! made the following statement 

 (p. 55):- 



*« Specimens similar to the preceding briefly noted forms 

 are often overlooked or considered unimportant by many col- 

 lectors; but to a student of morphological variations and pos- 

 sible specific change, they are extremely interesting. After 

 numerous accidental and natural changes have been illustrated 

 and described, embracing many genera and species, it will be 

 possible to generalize important biological facts relating to 

 the classification of species and manner of growth of the 

 organisms." 



The following descriptions and figures are a contribution 

 toward this end. 



* Presented by title before The Academy of Science of St. Louis, Novem- 

 ber 18, 1901. 



t Annual Report New York State Museum of Natural History. 36: 51. 

 1883. 



(143) 



