(is 
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., Pl. 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. 
iter dsea pulse-on Wecember 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 fleod (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 
