1915] Interesting Western Odonata 299 
thruout the year, so that the springs in western Canada, in 
which Argia vivida has been taken are probably the warmest 
waters in that region, comparing not unfavorably in warmth 
with springs of California and even Mexico. Thus by inhabit- 
ing springs this little subtropical Argia easily maintains itself 
far beyond the usual limits of members of its genus. Its 
vertical distribution is equally as great as it occurs from sea 
level up to 6,000 feet, where it is found in springs on the shores 
of Lakes Tahoe and Donner. 
An interesting observation in this connection is that Argia 
emma, the warm stream species, occurs also at this altitude, 
being found in the Truckee River at the outlet of Lake Tahoe. 
This is explained by the fact that the Truckee River, tho a 
mountain torrent and at an elevation of 6,000 feet is really a 
warm stream, because its supply comes from Lake Tahoe, 
which never freezes over. The great depths of this lake are 
filled during the summer with a body of water of 39° or more 
in temperature. (Actual measurements in August show 40° 
or more except in extreme depths). Tho the surface chills 
during the cold season, the lake waters are constantly turned 
over by the winter winds, bringing the warmer waters to the 
surface, where they keep the Truckee River supplied thruout 
the cold months with water several degrees above freezing. 
Another Agrionine with unusual habits is Enallagma clausum. 
This is an inhabitant of the desert and seemingly enjoys its 
life in the alkaline ponds of this barren region. It is found 
in the intermountain country from the Columbia Valley to 
Nevada. Several species of this large genus are stagnant water 
species and some of these in the West live in ponds with a slight 
alkaline content, but clausum goes beyond them all and breeds 
in water strongly saline, for it is found breeding in large numbers 
in the shallow edges of Pyramid Lake, Nevada. This is one 
of those salt lakes in the midst of the Nevada desert which 
have been left by the gradual drying up of Lake Lehontin. 
While the alkalinity of Pyramid Lake water is but about one 
tenth of that of sea water, it is very near the maximum that 
can be endured by various brackish water species. Sea water 
has a density of 1.026. Osburn (Am. Nat. June, 1906), has 
shown that various species of odonate nymphs found commonly 
in brackish coast ponds can endure a density of not more than 
