Introduction 



It is the purpose of the present volume to furnish to those inter- 

 ested in Illinois fishes a reliable guide to a knowledge of the species, a 

 careful account of their local and general distribution and of their re- 

 lations to their environment, a correct idea of the function and relative 

 importance of the different species in the general system of aquatic 

 life, and a fairly full summary of their habits and utilities so far as 

 these are now known. To this end the species have, with very few ex- 

 ceptions, been described anew from the specimens of our collection, 

 with due use, however, of descriptions already extant ; analytical keys 

 have been made, adapted, or selected, with special reference to the 

 Illinois species ; and our data of geographical and local distribution 

 and of ecological situation and relationship have been analyzed, to a 

 considerable extent, by statistical methods. 



The collections and field observations of Illinois fishes upon which 

 this report is based were begun by the senior author in 1876, and 

 were continued by him and by a considerable list of assistants, at 

 rather irregular intervals, to 1903. With the establishment of the 

 Illinois Biological Station on the Illinois River at Havana in 1894, 

 field work in ichthyology became more nearly continuous than' had 

 previously been possible. An especially interesting study was made 

 at Havana during the winter and spring of 1898 and 1899 by Mr. 

 Wallace Craig, an assistant of the State Laboratory, to whom was 

 assigned the duty of making systematic collections at fixed points 

 by the uniform use of identical apparatus at each, determining, 

 counting, and recording all the species obtained in each situation. 

 It was the object of this investigation to apply, in the field of ichthy- 

 ology, the quantitative method which had been used with distin- 

 guished success in the study of the plankton of the Illinois River 

 and adjacent waters at the Havana Station. During the summer of 

 1899 field work was transferred to Meredosia-with Mr. H. A. Surface 

 in charge, and later it was taken up by Mr. Thomas Large at Mere- 

 dosia and Ottawa, to which latter place the "station equipment was 

 transferred in 1901 . Extensive wagon-trips were made from time to 

 time through various parts of the state for a study of the fishes of the 

 smaller streams, the most important of them in 1899 by Mr. Large, 

 to whom we are indebted for the field determination of many of our 

 specimens and for numerous descriptive notes on the waters and 

 situations visited. 



