292 



once in the Saline. The ecological relationships of the species 

 are likewise very different, phoxocephalus showing a much 

 stronger tendency than fusiformis to the larger streams. It oc- 

 curs, for example, according to our data, in rivers in 63 per 

 cent, of the cases, as against 13 per cent, for the other species. 

 It also prefers swift to moderate water much more strongly, 

 if I may judge from the small number of collections for which 

 this factor was recorded, the ratios for swift water being 87 per 

 cent, for phoxocephalus and 22 per cent, for fusiformis. A cor- 

 responding difference is seen in respect to the character of the 

 bottom, 66 per cent, of our collections of fusiformis coming 

 from waters with a muddy bottom and only 6 per cent, of those 

 of phoxocephalus. 



Boleosoma nigrum and Etheostoma jessiw (1446 and 1474), 

 with their coefficient of .99, may serve as an example of species 

 similarly distributed but essentially indifferent as associates, 

 a coefficient of 1, it will be remembered, indicating a neutral re- 

 lation. A glance at the distribution maps of the species shows 

 at once some notable differences. Boleosoma nigrum, the most 

 abundant of our darters, and taken by us in two hundred and 

 thirty-six collections, has virtually the same geographical dis- 

 tribution as the other species, but it is represented in the larger 

 rivers in very much smaller ratio. The marks of local distri- 

 bution for the more abundant species are widely and rather 

 uniformly scattered over the map, with but few on the larger 

 streams, while those of the less abundant species are strung, like 

 beads, along the principal rivers of the state. On the other 

 hand, neither species is definitely excluded from either the ter- 

 ritory or the situations of the other, as may be seen by a com- 

 parison of the figures for them given in Table VI. 



Turning now to pairs of species with extraordinarily high 

 associative coefficients, I may call attention first to Etheostoma 

 zonale and Etheostoma coeruleum (1461 and 1477), whose coeffi- 

 cient reaches the remarkable figure of 8.38. The general dis- 

 tribution of these species is substantially the same, except that 

 EtJieosto)ua coeruleum has a greater development to the south. 

 Etlieostuma zonale is much less numerous than coeruleum, but 



