There are two main (irainat^e area.s, one, very .small, in the 

 northern part of the state, draining into Lake Michigan, and 

 the other, including the larger part of the state, draining into 

 the Mississippi River hy way of the Illinois. Kock, Fox, Desplaines, 

 Kankakee, Wabash, and Ohio, and other rivers and streams. 

 When the state is more thoroughly explored conchologically it 

 will probably be found that its mollusks will show peculiar 

 geographical variations due to its extent through five and a half 

 degrees of latitude (from 37" to 42^°). 



While the literature relating to the Mollu.sca of Illinois is 

 rather extensive, it is a singular fact that not one catalogue 

 has been puldished which gives a list of all of the species of 

 the state. Some of the more extensive catalogues which have 

 been published are mentioned below. 



In 1854 Mr. H. A. Ulffers published a list of the Mollu.sca 

 of Southern Illinois inthe Tran.sactions of the Illinois Horticul- 

 tural Society (Vol. I., p. 610). This included 87 species. Of 

 these, 14 are now considered synonyms. 



In 1871 Mr. John Wolf pnl)lished his "Catalogue of the 

 Shell-bearing Mollusca of Fulton County, Illinois," inthe Amer- 

 ican Journal of Conchology (Vol. VI., p. 27), listing 138 spe- 

 cies, of which 8 are now considered synonyms. 



In 1874 Mr. W. W. Calkins li.sted the Mollusca of Northern 

 Illinois in the Cincinnati Quarterly Journal of Science (Vol. I., 

 p. 321). This list included 129 species, of which but 6 are 

 now cousidei'ed synonyms. The same author, in the Proceed- 

 ings of the Ottawa Academy of Sciences for 1874. enumerates 

 105 species as occurring in La Salle County. 



In 1887-89 Mr. William A. Marsh enumerated 110 species 

 of land and fre.sh-water shells as found in Mercer county, his 

 lists being pul)lished in the Conchologist's Exchange (Vol. I. and 

 II.) and in the Nautilus (Vol. III.). Several of the species listed 

 are now considered synonyms. 



Dr. W. S. Strode (Nautilus, Vol. V., p. 61, American Natur- 

 alist. Vol. XXVI., p. 495) enumerates 35 species, mo.stly Unios, 

 from Spoon Kiver, near Bernadotte. 



