75 



nated in March. Rising floods thus do not favor the development 

 of Dinobryon in channel waters of the Illinois. 



The interval of collection in 1894-95 is too great to trace the 

 seasonal fluctuations of Dinobryon, though there are indications of 

 a maximum pulse on April 29. In 1895-96 there is^ a slight de- 

 velopment in November prior to the rise of December, in which 

 Dinobryon again disappears. A slight pulse of 3,192 appears on the 

 declining flood (Pt. I., PI. X.) on January 25, and declines again 

 with the rise in February to reappear on February 20 at 42,588. 

 Another decline in Dinobryon attends the rise in river levels in 

 February-March, and after a fortnight of falling levels a third 

 pulse of 2,531,280 is seen on March 17. Two other pulses attend 

 the decline of this flood, one upon April 29 (800,064) and the other 

 on May 18 (339,624). On the decline of the June rise of this year a 

 late and unusually large pulse for the season appears (June 11) at 

 2,438,400. An examination of the hydrograph will indicate that 

 almost without exception these pulses attend the run-off of im- 

 pounded backwaters after recent invasion, or, as on April 29 and 

 May 18, after a temporary check in the run-off. During those 

 times when the channel contributes to the backwaters, that is, dur- 

 ing rising floods, Dinobryon declines in numbers ; and, on the other 

 hand, it reaches its greatest development in channel waters during 

 the run-off of the flood. 



In 1896-1897 the interval of collection (Pt. I., Table III.) is 

 again too great to trace satisfactorily the fluctuations of Dinobryon. 

 There is a pulse on December 3 of 157,609 and on April 27 of 

 172,800. 



In 1897-98 Dinobryon appears first on December 7, with a pulse 

 of 1,807, 200, during a period of low water and ice blockade with no 

 backwater contributions. It declines, and after December 21 does 

 not again return until March 22, when an isolated record appears. 

 The vernal pulse begins April 19 and culminates May 10 at 84,- 

 841,600 on the declining spring flood (Pt. I., PL XII.). Dinobryon 

 declines at once during a fortnight of rising water, and two minor 

 pulses on the decline of the flood one on June 7 of 70,400 and one 

 on June 28 of 219,840 complete its vernal cycle. 



The hydrographic conditions in 1898-99 were very different from 

 those of the preceding season, and we find a marked change in the 

 seasonal occurrence of Dinobryon. From November to March 



