500 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.52. 



This pair, the type and allotype, are dried alcoholics. My mem- 

 ory is that in life the female had the pale colors on the thorax and 

 abdomen pale green. 



CELAENURA DENTICOLLIS (Barmeister). 



This smallest of western dragonflies occurs throughout the warmer 

 valleys of California, Nevada, Arizona, and northwestern Mexico. 

 My data for Mexico are from Calvert.^ This species is foimd com- 

 monly on the high central plateau of Mexico, where the farthest south 

 record is on the slope of Mount Orizaba at an elevation of over 6,000 

 feet. It does not occur on the lower land of the east coast but it is 

 found down the west coast, although not as far south as it occurs on the 

 cooler plateau. In Cahfomia and Nevada it is found from sea level 

 up to 4,400 feet. It is, in the latter States, distinctly a spring stream 

 species, though in southern Cahfornia it is found about almost any 

 pennanent, sluggish water. Many of my northern records are spring- 

 stream records. In the hot Sacramento VaUey I found it at Colusa, 

 which was as far north as I went. At Cahstoga, California, it was very 

 abundant in the cooler of the warm outlets of the Hot Springs. It oc- 

 curred in a spring stream at Auburn, California (3,400 feet elevation), 

 on the east side of the Sacramento VaUey. At Golconda, Nevada 

 (elevation, 4,400 feet), perhaps the coolest climate in which I found 

 it, denticollis flourished in a warm spring where freezing weather could 

 have httle influence on the nymphs. In none of the locahties men- 

 tioned in the preceding, with the exception of Golconda, Nevada, 

 where the nymphs are protected from the freezing weather by the 

 warm water, are there heavy frosts with any severe winter weather. 



Its distribution then indicates that it is distinctly a subtropical 

 insect, but just as distinctly that it is not tropical. It is with equal 

 distinctness confined to the semiarid and arid regions. This inter- 

 estmg distribution from sea level on the northern boundary of its 

 habitat to the great elevation on its southern boundary is found in 

 many other western Odonata, many species having very definite tem- 

 perature limits. 



The habits of this species are in general ischnuran but indicate 

 greater feebleness. Early in the mornmg it is found in the sedges and 

 grasses bordering the water but during the heat of the day it spends 

 the greater part of its time over the surface of the water, usually 

 seated on trash or aquatic vegetation. At Calistoga I had an excellent 

 opportimity of observing its habits because of its great abundance. 



Here several nymphs ready to transform were taken from the trash 

 around the edge of a warm spring and the exuviae were common on 

 the grass stalks fringing the water. I caught none in the act of trans- 

 forming, as it was cold rainy weather, but I feel reasonably certain of 

 the identity of these nymphs. 



1 Biol. Amer., Neur., pp. 126, 387. 



