284 



and sections of the state, are inclusive of all our collections; 

 but in many cases data are wanting definitely descriptive of the 

 waters and the situations from which the collections were made. 

 This is owing to the fact that the present use of these materials 

 was not foreseen in the beginning of our collection period, nor, 

 indeed, until the greater part of the field work had been done, 

 and the records of the earlier years are consequently often in- 

 complete for the present purpose. Later, collectors were instruct- 

 ed to make full descriptive notes, from the ecological stand- 

 point, of each body of water visited and of each location at 

 which a haul of the seine was made, and the whole body of the 

 data of local distribution and ecological preference is such that 

 if used with due discretion it may be expected to throw con- 

 siderable light on the associative relationships of this little 

 group of fishes. 



These data have been worked out, in the same manner as 

 in the preceding section of this paper, in the form of percent- 

 ages of frequency of the occurrence of each species in each ge- 

 ographic or hydrographic subdivision and in each ecological 

 situation. As the numbers of collections made have varied 

 widely for the several areas and situations, those from one be- 

 ing often many times as numerous as those from another, it was 

 necessary to reduce the frequency ratios of the several species 

 in each area to a common standard for comparison. These num- 

 bers have been equalized, and confusing discrepancies removed, 

 by reducing the collection data to percentages of the same base, 

 which, for convenience, has been made one hundred collections. 



Discussion of Ecological Tables. 



If equal numbers of miscellaneous collections had been 

 made from each situation, and if the total number of collec- 

 tions were such that any given darter had been taken one' hun- 

 dred times, what number or percentage of these collections of 

 darters would have come, according to my present data, from 

 each of the situations represented? 



The figures in Table VI. are answers to this question; and 



