Muttkowshi—The Fauna of Lake Mendota. 
397 
goptera, Aescliniiiae^ and many Cordulinae. But even those 
species which lay their eggs free on a substratum (sand^ mat¬ 
ted algae, scums, etc.) or in the open water are largely con¬ 
fined to the more quiet habitats. This may be due to the food 
varieties, more of which are offered in ponds, swamps, and 
quiet streams, than in turbulent waters. However, it is impor¬ 
tant to point out that it is not the respiratory factor which re¬ 
stricts the Odonate lake complex, but purely that of food and 
a special habit, oviposition. 
Habitat relations, general form, and method ot locomotion 
are closely interrelated in the Odonata. This relationship is 
expressed in table 2. Both positions at rest and methods of 
locomotion are combined in order properly to designate the 
main types of larvae. Many genera or subfamilies are com¬ 
paratively restricted; thus, the Zygoptera in general, and al¬ 
so Gomphinae and Petalurinae, are poor swimmers, and have 
primarily a sedentary, ‘^clinging’’ mode of life, and the Gom- 
phinae and Petalurinae a burrowing habitus. (See p. 471.) 
Argia putrida (Hagen). 
The nymph of this species is easily recognized from its stout, 
depressed form; it is slate-colored, with wdiite-tipped caudal 
gills. It belongs to the category of rock-clingers and is one 
of the characteristic forms of turbulent waters. While it oc¬ 
curs in the rocky areas of the lake, its optimal habitat seems 
to be in rapids. 
Enallagma antennatum (Say). 
This species is fairly abundant in the lake, together with 
Ischnura verticalis. It is a true plant dinger. Other species 
of Enallagma occur in restricted areas of the lake, especially 
where a river fauna enters or a swamp fauna lies nearby. In 
such spots Enallagma hageni, carunculatum, ebrium, signatum, 
and pollutum may be found in fair numbers. No Lestinae oc¬ 
cur in the lake, but they are abundant in spring-fed ponds and 
in clear creeks. 
Gomphus fratenius (Say). 
The nymph burrows into the sand or rubble at the point 
where wave-action is strongest, hence at the breaker-line. 
Like Argia putrida, it is much more abundant in rapids than in 
the lake. 
