285 
Since the aquatic insects of these collections are being studied by 
others, with reference to publication in this Bulletin (see Hart,’95, 
and Needham and Hart, ’01), only passing notice of the more 
important representatives appears in this connection. 
EPHEMERIDA. 
Ephemerid larve, as a rule in early stages, were found singly 
or in small numbers in the channel plankton in the warmer months, 
April—October, at temperatures above 56°. Since these occurrences 
were with few exceptions in stable hydrographic conditions, it seems 
probable that the younger larve of this order may adopt, at least 
temporarily, a limnetic habit. Specific identifications of these 
larvee were not made. 
HEMIPTERA. 
Corisa (?) sp.—Average number, 37. A small hemipterous 
larva doubtfully referred by Mr. C. A. Hart to Corisa, was taken 
~ with some frequency but in relatively small numbers in the plankton 
during the summer months. Of the 36 occurrences 27 fall in 
June-August, 2 in May and 3 in September, 2 in January, and 1 each 
in October and November. It thus appears in the temperature 
extremes, but exhibits a great predominance in the season of maxi- 
mum heat. There is no marked increase in its frequency or numbers 
in years of more disturbed hydrographic conditions. Its numbers 
are always small and somewhat erratic. Adult Corisa, as well as 
many other aquatic Hemiptera, were found in plankton collections 
singly and infrequently. 
DIPTERA. 
This group of insects is abundantly represented in the plankton, 
but in all cases by larval or pupal stages. 
Clironomus spp., larval stages.—Average number, 124. Larve 
in various stages of development from that immediately after 
hatching to that approaching pupation were found in channel 
plankton. They occur in considerable numbers in the ooze in the 
river bottom, but appear to abandon the limicolous for the limnetic 
habit, temporarily at least, as a result of hydrographic or other 
disturbances. There is evidence from their relative numbers in 
