J32 



Illinois N.aturai. History Survey Bulletin 



\'.)1. 28, Art. 2 



Table 7. — Species showing increases in frequency of occurrence (per cent of stations in 

 which each species was taken) in Champaign (bounty in three surveys; for each species is given 

 the number of drainajjes in whicli it was taken in each surve\. 



they are peripheral populations, N. ruhel- 

 lus reaching its southernmost point of dis- 

 tribution, at least in eastern Illinois, 

 within Chainpai<^n County, and the other 

 two reachini: their easternmost limits of 

 distribution in the county. A', ruhellus ap- 

 pears to have extended its ran^e south- 

 ward into the county between 1899 and 



1928 and to have replaced the allied N . 

 otheritioides in both drainages where ru- 

 hellus was found in 1959. A', dorsalis has 

 been known in the county for at least 60 

 \'ears; there is evidence from another 

 source, in addition to the Champaign 

 County data, that its range is gradually 

 shifting eastward. A similar trend is 



Table 8.— Species showing decreases in frequency of occurrence (per cent of stations in 

 which each species was taken) in (Champaign County in three surveys; for each species is given 

 the number of drainages in which it was taken in each survey. 



♦Includes Opsopoeodiis emiliae and Hybopsis aestivalis recorded by Large (1903:15. 19) 



