Lake Maxinkuckee, Physical and Biological Survey 41 



THE MOLLUSKS 

 THE UNIONID^ 



During the study of Lake Maxinkuckee considerable attention 

 was given to the mollusks, particularly the freshwater mussels or 

 Unionidae. This was justified by the rapid and astonishing de- 

 velopment of the pearl button industry in America which is de- 

 pendent upon the shells of mussels for its raw material. The 

 recent discovery by Lefevre and Curtis of methods whereby com- 

 mercially valuable species of mussels are now successfully propa- 

 gated artificially, adds special interest to these mollusks. Recent 

 studies and discoveries relating to the formation and artificial pro- 

 duction of pearls in freshwater mussels may also be mentioned as 

 showing the importance of careful study of the taxonomy and life 

 history of the Unionidse. 



LAKES AND PONDS AS THE HOME OP 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 somewhat dwarfed. Of about 84 species of mussels re- 

 ported for the State of Indiana, only about 24 are found in lakes, 

 not all of these in any one lake, and several of them but rarely in 

 any. Of the 24 species occasionally found in lakes, but five are 

 reported only in lakes, and only three or four of the species com- 

 mon to both lakes and rivers seem to prefer lakes. 



In rivers, the essential feature favorable to the development of 

 mussels is the current; and in the rivers the mussel beds reach 

 their best development in the riffles, where the current is strong- 

 est. The importance of the current to the well-being of the 

 mussels is indicated by the position these mollusks naturally as- 

 sume in the beds, the inhalent and exhalent apertures of the crea- 

 tures being directed up-stream against the current. The im- 

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

 inations show that the mussels of the plankton-rich lakes and 

 ponds usually contain more food material than those of rivers. 

 The current gives the river-mussels the advantage of a constant 

 change of water, which means a more abundant supply of oxygen, 

 and doubtless a more varied supply of mineral matter, from the 

 various sorts of soil through which the river flows. 



The current is also probably of considerable importance in as- 

 sisting in the fertilization of mussels, one of its functions being 



