298 Annals Entomological Society of America [Vol. VIII, 
which lies each clutch of eggs, dies after the eggs have hatched 
and this produces a scar, which from year to year increases 
laterally with the growth of the stem. Sometimes the scars 
of contiguous ovipositions run together and girdle a willow, 
so this dragonfly may be classed technically among those 
insects injurious to timber. 
The nymphs of this dragonfly, which are probably among 
the largest of the Zygopterus nymphs, are peculiar in being very 
free swimming. On the Yakima River I worked for an hour 
with a rake without catching a single specimen, tho I knew from 
their emergence that they must be abundant. Later in Cali- 
fornia I was astonished to discover that certain ‘‘schools of 
minnows”’ were the agile nymphs of Archilestes fleeing enmasse 
from the dragonfly collector. On closer observation they 
were found to spend most of their time resting quietly on 
submerged objects, but on the approach of danger they fled 
precipitously to deeper water. Swimming was accomplished 
by a vigorous undulatory motion, in which the large caudal 
gills seemed of great assistance. 
One of the peculiarities of the western Odonate fauna is 
the small number of Argias. This is a genus of 60 or more 
species the greater number of which are found in the American 
tropics. Eight or more occur in the eastern states, but only 
two are found west of the Rockies, excepting, of course, the 
various southern species limited to the Mexican border. Tho 
essentially a tropical genus, one of the two western species, 
Argia emma, is common as far north as central Washington, 
and the other Argia vivida, is found even as far north as Canada. 
The extraordinary northern distribution of Argza vivida, which 
occurs also as far south as southern Mexico, seems explained 
by its peculiar habits. All the species of Argia as far as is 
known, live in very fresh water, the majority of them being 
stream species. Such is Argia emma, which is found in the 
majority of the warm perennial streams of the west. But 
Argia vivida has a special preference for springs and the boggy 
streamlets flowing from them. This species is frequently 
collected on larger streams and ponds, but in such cases, when 
traced to its origin, is found to be emerging from some nearby 
spring. Now springs do not freeze, as their waters, originating 
deep in the ground, maintain a fairly uniform temperature 
