21)2 



once in the Saline. The ecological relationships of the species 

 are likewise very different, jilio.niccjilKihis showing a much 

 stronger tendency than Jiisi/'onii is to the larger streams. It oc- 

 curs, for example, according to our data, in rivers in (58 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 1 may judge from the small number of collections for which 

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

 cent, hn- j)li(i.t(ic('plHihi.s i\iu\ 22 per cent, for /'».s//orH(/.s'. A cor- 

 responding difference is seen in respect to the character of the 

 bottom, 6(5 per cent, of our collections of fns/Joniiis coming 

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

 of pliiKroct'phdIus. 



no/cnsoiiKi niijruiii and EtIieostoiiDi yV.s.s/r/' (1446 and 1474 ), 

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

 simihirly distributed but e.sseutially 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. Bo/eosoinn jiii/nim. 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 these 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 hrst to Etlifusfviiui 

 zonale and Etheostomn rirnilpum (1461 and 1477), whose coeffi- 

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

 tribution of these species is sulxstantially the same, except that 

 EtJu'ostoiitd cwni/fioii has a greater development to the south. 

 Etheostoma zonule is much less numerous than (■(enilenm, but 



