294 



The next coefficient in order of size, that of Hadroptenis 

 phoxocep/ialiis and Aii/Dioo'i/ptd pcJlKcida (1418 and 1450), is 

 4.95. These species are virtually identical in general distribu- 

 tion, pcl/ucida being, however, comparatively scarce. The two 

 species have been taken in ten of the seventeen localities in 

 which pcUiie'uJa was found, and have occurred conjointly eight 

 times in the ninety-six collections containing one or the other. 

 In general ecological relationship they are very closely similar, 

 both occurring infrequently in the larger rivers, and in smaller 

 rivers more frequently than in creeks. Aniniocri/pfa 'pelliwida 

 has not been taken at all in lakes and ponds, and phoxoceph(dt(S 

 only to the amount of 3 per cent. Both are rapid-water spe- 

 cies, and strongly prefer streams flowing over rock and sand 

 to those with muddy bottoms. 



Hadropteriis aspro and Ammocrypta pelluc Ida {1^21 and 1450), 

 with a coefficient of 3.97 based on their twelve jointoccurrences 

 in one hundred and sixty-six collections, wei'e taken from the 

 same localities in ten cases of a possible seventeen. Aniino- 

 cri/pfo peUiir'tda, although much the less abundant, »is distrib- 

 uted in general precisely like aspro, except that it does not show 

 so marked a preference as does the latter species for the east- 

 ern part of the state. With respect to the character of the 

 streams in which these species are most generally found, the 

 ratios are unusually similar, pelhicida occurring, however, ac- 

 cording to our data, more commonly in the larger rivers, and 

 aspro more frequently in creeks. Neither has been taken by 

 us in lakes or ponds. The ratios of preference for waters with 

 a clean bottom are 84 per cent, for each. 



Perc'ni(( aiprodes and Efheosfonia zonale (1417 and 1461) were 

 taken together four times in the eighty-eight collections con- 

 taining either or both. Their associative coefficient is 3.55. 

 Their general distribution is different in the fact that caprodes 

 is the more alnindant in the central and southeastern parts of 

 the state. They were collected from the same localities seven 

 times out of a possible thirty. In ecological relationships they 

 are only fairly similar. Both occur in the larger rivers, but 



