SOME ABNORMAL AND PATHOLOGIC FORMS OF FRESH-WATER 

 SHELLS FROM THE VICINITY OF ALBANY, NEW YORK. 



BY CHARLES E. BEECHEK. 



Monstrosities among fresh- water shells are not infrequent and are 

 interesting as illustrative of the cause of natural or accidental de- 

 formity. A large proportion of abnormal or pathologic forms is found 

 in exposed situations, where the shells are subject to varying condi- 

 tions of water and materials brought by currents or otherwise. The 

 annual draining and cleaning of the canals renders the contained or- 

 ganisms liable to many accidents. It is likewise found that in the 

 vicinity of a ford or watering-place for cattle, many of the uniones bear 

 the marks of injury. It is, while the animal is repairing these in- 

 juries and adapting itself to changing conditions of water and deposits, 

 that most of the malformations in its shell are produced, and it is quite 

 seldom that a shell is found which has been deformed by the atrophy 

 or hypertrophy of any of the animal organs. These malformations 

 are occasionally transmitted and their degree is often augmented by 

 the action of the law of accelerated heredity, as applied to the mollusca 

 by Professor Alpheus Hyatt.* 



It is convenient to consider abnormalities as natural or accidental. 

 Natural changes are usually produced by the action of gravitation, 

 adaptation to modified habitats or by changes in the forms of the organs. 

 The effects of gravitation are noticed mainly in those univalves which 

 live at or near the surface of the water and, therefore, necessarily carry 

 the weight of the shell at a disadvantage. 



Accidental deformities are always the accompaniment of an attempt 

 by the animal to repair injuries which it has received. If the form of 

 the shell has been altered, the animal will accommodate itself to this 

 alteration ; and, on the contrary, if permanent injury or malformation 

 has been produced in the soft parts of the animal, the accreting test 

 will gradually adjust itself to this change in those parts. 



* The Genesis of the Tertiary Species at Steinheim, by Alpheus Hyatt ; page 27, Anniver- 

 sary Memoirs of the Boston Society of Natural History, 1860. 



