GEOIvOGY OF r.A SAIvIvE COUNTY. 93 



THE MOLLUSCA. 



Mollusks are animals having- soft bodies without 

 a hard skeleton, breathing- by g-ills, and is by far the 

 larg-er number of species covered by a shell. They are 

 of three kinds, not having- a shell like the garden slug-; 

 second, shell usually coiled, of one piece, like the snail; 

 called univalves third, shell of tv^^o parts or pieces, 

 called valves, like the oyster and clam, called bivalves. 



They are also divided into Land, Freshwater and 

 Saltwater Mollusks. 



The'MoUusca of La Salle county belong to all three 

 divisions or groups of the first arrangement and to the 

 first and second of the second. 



The land mollusks are lovers of shade and damp- 

 ness, and as the countr}^ is settled, wet lands drained 

 and forests destroyed, no doubt many species will be- 

 come extinct; some are already rare, but those living 

 in the water will probably hold their own. We ob- 

 serve, however, that the drainage of coal mines into 

 the Big Vermillion, at every season of low water, kills 

 off the unios of that stream, and at present very few 

 are found in it. 



The following notes on the mollusca of this county 

 are largely taken from Mr. William Wirt Calkins' 

 "Land and Presh Water Shells of La Salle County, 

 Illinois," published in 1874, as Proceedings of "The 

 Ottawa Academy of Sciences," an organization that 

 practically ceased to exist about 1881, when it placed 

 its library and cabinet in the care of the trustees of 

 the Ottawa Tp. High School, since which time it has 

 held no meetings, and the members have, most of them, 

 died or removed from the city. Cannot La Salle Co. 

 support one Scientific Society? Is there not work in 

 this great county for one? 



Mr. Calkins is in no way responsible for the pres- 

 ent form of this paper. It has been considerably al- 

 tered from the original. 



