102 FISHES OF ILLINOIS 



.21 of the number which would have contained it if it had been 

 uniformly distributed. From the entry in the third column it 

 will be seen that in small rivers the abundance of Campostoma 

 anomalum was a little more than 2^ times as great as if the 

 species had been uniformly distributed; and from the fourth 

 column, that in creeks it was a little more than 3^ times as 

 abundant. The number of its occurrences in lowland lakes 

 was but .05 of the normal average, and in upland lakes the 

 species has not been taken by us at all. 



The seventh and tenth columns of these figures give the 

 numbers of collections for each species concerning which data 

 were recorded available for computing their relative frequencies 

 in rapid and quiet waters, and on clean and soft bottoms. 

 From the figures in the last six columns of the table we learn, 

 concerning Campostoma, that 65 collections give us a coefficient 

 of 1, 7 for a rapid current as compared with .59 for quiet water, 

 equal frequency in the two situations being, as before, repre- 

 sented by 1. The strong preference of the species for a clean 

 bottom over one of mud is shown by the last two numbers, 

 applying to 105 collections, the two coefficients being respec- 

 tively 3.26 for a clean bottom and .31 for one of mud. 



In Tables II. to V., relating to minnows and the environ- 

 ment, the species most characteristic of each situation are 

 brought together in lists arranged in the order of the size of 

 their coefficients of frequency. The remaining lists refer to 

 peculiarities of territorial distribution within the state. 



The following keys and descriptions of Cyprinidce have been 

 designed for use with a minimum of attention to obscure charac- 

 ters and to those difficult of access. However, it will be neces- 

 sary in all cases for beginners in ichthyology to ascertain by 

 dissection whether their specimen belongs to the long- or the 

 short-intestined class of minnows (see key to genera of Cy- 

 prinidce). It is possible, however, to dispose entirely with the 

 use of dental characters in the indentification of minnows, 

 and our keys have been constructed with that fact in view; 

 although, for the purpose of completeness and for the aid of 

 those who may wish to carry their studies further than the sim- 

 plest artificial key will take them, we have in every case included 

 a reference to the number and form of the pharyngeal teeth.* 



* In Illinois Cyprinidce the main row of teeth on each pharyngeal bone contains 4 or 5 teeth; 

 inside of this main row is a so-called "lesser row " which may contain 1 or 2 teeth or be un- 

 represented altogether, in the latter case being designated "0" in the formula. For example, 



