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The Unionid^ of Lake Maxinkuckee. 



By Barton Warren Evermann, 



California Academy of Sciences, San Francisco, 



and 



Howard Walton Clark. 



U. S. Biological Station, Fairport, Iowa. 



During the physical and biological survey of Lake Maxinkuckee 

 carried on by the writers at intervals from 1899 to 1913, under the 

 auspices of the United States Bureau of Fisheries, considerable atten- 

 tion was devoted to the freshwater mussels or clams (Unionidae) in- 

 habiting that lake. This was justified by the rapid and astonishing 

 development of the pearl button industry in America, which is dependent 

 upon the shells of the mussels for its raw material. The recent develop- 

 ment of methods whereby several species of Unionid^ are now success- 

 fully propagated artificially adds special interest to the study of these 

 mollusks. 



Lakes and Ponds as the Home of Mussels. 



Generally speaking, lakes and ponds are not so well suited to the 

 growth and development of mussels as rivers are; the species of lake- or 

 pond-mussels are comparatively few, and the individuals usually some- 

 what dwarfed. Of about 84 species of mussels reported for the State 

 of Indiana, only about 24 are found in lakes, and not all of these in 

 any one lake, several of them but rarely in any. Of the 24 species 

 occasionally found in. Indiana lakes, but 5 are reported only in lakes, 

 and only 3 or 4 of the species common to both lakes and rivers seem to 

 prefer lakes. 



In rivers, the essential feature favorable to the development of mus- 

 sels is the current; and in rivers the mussel beds reach their best devel- 

 opment on riffles, where the current is strongest. The importance of the 

 current to the well-being of the mussels is indicated by the position these 

 mollusks naturally assume in the beds, the inhalent and exhalent aper- 

 tures of the creatures being upstream against the current. The im- 

 portance of the current is not merely as a bringer of food; examina- 



