Mutthowski—The Fauna of Lake Mendota. 
415 
In fish taken from the Yahara Canal Gyrinus larvae are 
rare, while adults, in spite of their presumably noxious eman¬ 
ations, are more frequent. 
Family Haliplidae. 
Haliplus ruficollis DeGeer; Peltodytes edentulus LeConte; 
Peltodytes duodecimpunctatus Say. 
These three species are common in the lake, both in larval 
and adult form (except the larva of the last, which I have not 
found). The larvae are water-breathers, while the adults can 
remain submerged for considerable periods. The larvae are 
microphagous on filamentous algae and are not restricted in 
their distribution save by that of their sheltering plants. In 
creeks, basins, and elsewhere the larvae may be quite abundant. 
Among the Cladophora and other algae just below the Yahara 
spillway, Haliplus ruficollis larvae are especially abundant and 
form a favorite item in the food of fish. 
Family Hryopidae. 
There is no other insect family with aquatic representatives 
that offers as many points of interest as the Dryopidae. Adap¬ 
tation to an aquatic life has reached its highest development 
among them, both in the larvae and in the adults. As will be 
seen from table 4 there are two groups according to degree of 
aquativeness, both of which have in common holaquatic larvae 
and terrestrial pupae, but differ in the aquatic habits of the 
adults. (See p. 473). 
Of the five genera given, Limnius is not represented in the 
American fauna, its place being taken by Stenelmis. Psephe- 
nus lecontei and Stenelmis crenatus were bred in large quan¬ 
tities, while a third species (a larva resembling that of Elmis 
somewhat and which I believe is Dryops lithophilus) did not 
reach pupation in the various cultures. 
Stenelmis crenatus Say; Elmis vittatus Mels. 
The larvae of Stenelmis crenatus resemble those of the Euro¬ 
pean Limnius troglodytes. In color they range from a light 
brown to a deep black, and it was thought at first that two 
species were represented in the larval material. Extensive 
breeding proved the identity with Stenelmis crenatus. 
