ETHEOSTOMA 309 



Its ecological separateness from its nearest allies, notwithstand- 

 ing its close resemblance to them, is shown by our coefficients of 

 association of this species with the banded, the rainbow, and the fan- 

 tailed darters, the other relatively abundant species of its genus. 

 These are .37 for the first of the above-named species, .77 for the 

 second, and 1.27 for the third, an average of .8. to be compared 

 with the general subfamily average of 2.02, and with one of 5 .54, 

 which is the mutual associative coefficient of the three other species 

 of the group. It has, in short, been found by us in company with 

 the three other common species only about one seventh as frequently 

 as they have been found with each other. 



The species has occurred nearly three times as frequently in cen- 

 tral, and nearly twice as frequently in southern, as in northern Illi- 

 nois. Notwithstanding this indifferent distribution as to the kinds 

 of waters it inhabits, our data of situation indicate a decided prefer- 

 ence for a strong current and a bottom of rock or sand. It is a very 

 common species in the Illinois at Havana and Meredosia, 88 of our 

 collections having come from that situation, usually conspicuous by 

 the absence of other darters. 



It is reported outside Illinois from Devil Lake and Tiffin River, 

 Michigan, through Indiana and Iowa to Mississippi, Arkansas, 

 Oklahoma, Texas, and the Rio Grande, and also from the Etowah 

 River in Georgia. 



Its food consists of larvae of May-flies and Chironomus larvas, 

 taken by the specimens studied in about equal quantity. 



Females with large eggs were caught in the middle of March, but 

 others captured May 12 had not yet spaw^ned. Craig, however, 

 reports it spawning at Havana in April and May, 1898. Males still 

 retained their breeding colors in August, 1903. 



ETHEOSTOMA CGERULEUM Storer 

 (rainbow darter; soldier-fish) 



Storer, 1845, Proc. Bost. Soc. Nat. Hist., 47. 



J. & G.. 517 (Poecilichthys) ; M. V., 133: B., I, 71; J. & E., I, 1088; N., 34 (Poeci- 

 lichthys coeruleus and spectabilis) ; J., 41 (Poecilichthys variatus and spectab- 

 ilis); F., 64; L., 29. 



Length 2 inches; robust, rather deep and compressed, and back, 

 especially in males, more or less elevated ; depth 4.7 to 5 ; greatest width 

 about I greatest depth ; depth of caudal peduncle 2.1 to 2.5 in its 

 length. Color dark olive, overlaid with dusky to bluish (or brilliant indigo- 

 blue) bars and blotches; scales of sides each with a dark central spot, 

 these forming more or less longitudinal rows most distinct in females 



(21) 



