SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE. 



241 ^ 



A CONTRIBUTION 



HISTORY OF THE FRESH-WATER klGM 



NORTH AMERICA. 



BY 



HORATTO C. WOOD, Jr., M.D., 



PBOFESSOR OF BOTANY, AND CLINICAL LECTDRER ON DISEASES OF THE NERVOUS SYSTEM IN THE 

 DNIVERSITY OF PENNSYLVANIA; PHYSICIAN TO TUE PHILADELPHIA HOSPITAL, ETC. 



[accepted for publication, PEBr.UARY, 1S72.J 



