112 



THE NAUTILUS. 



difference may be due more or less to difference in the seasons 

 (weather) from year to year. 



The facts already obtained have an important bearing on legislative 

 action already taken or contemplated for the protection and preser- 

 vation of our fresh-water mussels. Unlike the song and game birds 

 and the mammals, no close season will serve to protect all of the spe- 

 cies. The taking of all clams under the fully adult size must be pro- 

 hibited to prevent their extermination by pearl-hunters and button 

 manufacturers. 



TABLE SHOWING GRAVID PERIODS OF THE UNIONID^E. 



The letter g indicates gravid individuals, n denoting that none 

 were found gravid, gn that some females examined were gravid, others 

 not gravid, either among specimens taken at the same time or in the 

 same month in different years. 



