300 Annals Entomological Society of America |Vol. VIII, 
1.003. Pyramid Lake water has a density of 1.00347 to 
1.00349. The broad sandy beach at the southern end of 
Pyramid Lake fairly swarms with the nervous imagoes of this 
species, and the females accompanied by the males oviposit in 
the masses of filamentous algae that float in the shallow edge of 
the water. 
Oddly enough Enallagma clausum shares its occupancy of 
Pyramid Lake with another dragon fly, a libelluline, Sympetrum 
corruptum, which just opposite to Enallagma clausum, instead of 
being a species restricted by special habits, is extremely adapt- 
able, in fact the dragonfly, which in the west, is found in a 
greater variety of environments than any other. Sympetrum 
corruptum occurs from the sea level to altitudes of 3,500 feet 
in Washington and 5,000 feet in California, and flourishes not 
only in all kinds of ponds, but in all streams except those very 
swift mountain torrents inhabited by Octogomphus and 
Cordulegaster. Thus it is interesting that the extreme environ- 
mental condition found in the salinity of Pyramid Lake has 
been mastered as it were thru opposite types of development; 
by extreme specialization in clausum for a life in alkaline water, 
and by an extreme generalization in Sympetrum corruptiun for 
a life in the greatest variety of waters. Both species flourish 
side by side and no other species was observed. 
Many interesting phases of odonate habits and distribution 
in the West are related in various ways to the very rugged 
topography of this region. In a half day one can go by train 
from sea level in the Sacramento Valley, with its Mexican 
fauna and sprinkling of tropical species, to an elevation of 6,000 
feet in the Sierras, where all odonate species are such as are 
found in Canada. These northern species are in various Ways 
adapted to endure the cold, which prevents the occupation of 
these high altitudes by multitudes of dragonflies that flourish 
in the sunshine of the warm valleys. <A special adaption, 
which permits one of these species to exist on this cold upper 
limit of odonate life was discovered while collecting about 
the McKinney Lakes, which lie on the divide west of Lake 
Tahoe, at an elevation of 7,000 feet. The species in question 
is the large blue Aeshna interrupta nevadensis. This is restricted 
to the summits of the Sierras having been found from an eleva- 
tion of 4,000 feet at Emigrant Gap to 7,000 feet on the McKin- 
