370 
IOWA ACADEMY OF SCIENCE 
their wing covers. Dytiscid larvae of at least two species were 
taken. These also are predaceous and the writer observed one 
larva of a large species which had seized a larva of a Tipulid 
fly larger than itself and into which it had sunk its long mandi- 
bles. Another of the same species gave chase to a May fly nymph 
and persisted for several minutes until the greater fleetness of 
the pursued enabled it to escape its enemy. 
2. Hydrophilidae. Four species of the Hydrophilidae, water 
scavenger beetles, were taken, of four genera: ^Hydrohius fus- 
cipes Linn., Helophorus lineatus Say, Philydrus cinctus Say and 
Cymhiodyta fimbriata Say. While these beetles swim about freely 
their food habits as scavengers confine their activities to the 
debris-covered bottom and on this account they must be placed 
in the bottom association. 
3. Staphylinidae. Two species of Staphylinidae, the short 
winged scavenger beetles, namely Tachyporus jocosus Say and 
Stenus sp? were taken from partly submerged masses of decay- 
ing leaves. These beetles are wholly terrestrial in their adapta- 
tions and must be included in the transition zone association. 
4. Heteroceridae. The burrows of Heteroceridae, the varie- 
gated mud-loving beetles, were observed on some of the small 
mudflats formed by silt deposition along the course of the stream. 
These beetles are one of the most characteristic forms of life on 
the mudflat and hence become important members of the transi- 
tion zone association. No specimen was taken. 
Diptera. — By far the greatest number of species prevailed 
among the forms of Diptera in their aquatic immature stages. 
Representatives of five families were taken as follows: Culi- 
cida 0 , Chironomidae, Tipulidse, Stratiomyiidge and SimulidaB. 
1. Culicidae — ^Mosquitoes. By far the most abundant forms 
of the Culicidae were the larvae of Culex which had made their 
first appearance in the pools in great numbers by April 17. 
Upon April 24 these had increased greatly in numbers and a 
very few had pupated. Microscopic materials are swept into 
the mouth and contain both plant and animal matter. These 
larvae belong to the free-swimming association although they 
are obliged to rise to the surface at intervals for breathing pur- 
poses. 
Coretha sp ? larvae were taken in small numbers on April 10, 
17, and 24, and pupae were added on the latter date. These 
2The species of beetles listed in this paper were determined by Prof. H. P. 
Wickham, of the State University. 
