516 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.52. 



of the Pacific slope while one other is recorded so far only from 

 Mexico and Central America. The western species are C. dorsalis 

 Hagen and C. diadema Selys. Dorsalis occurs in the coast mountains 

 from Sitka, Alaska, south to the San Gabriel Mountains at Los An- 

 geles, California. It is found up to an elevation of 4,000 feet on the 

 west slope of the Sierras in California but has never been recorded 

 from the eastern side of these mountains. Diadema is recorded from 

 the mountains of Arizona and northern Mexico. 



My records for Cordulegaster dorsalis are as follows: Stevens Creek, 

 Santa Clara County, California, May 31, a single fresh exuvia and 

 several grown nymphs were collected but no imagoes were seen; 

 July 7, eight males were observed; August 16, three males and one 

 female were caught, the latter while ovipositing. Zyante Creek, 

 Santa Cruz County, Cahfomia, July 9, numerous exuviae were found 

 but no adults were seen. Napa Asylum Grounds, Napa County, 

 Cahfornia, June 8-9, six males were taken on a small mountain stream 

 flowing from the Hospital reservoir; no females were seen. In Mr. 

 Fordyce Grinnell, jr.'s, collection is a male taken on the Arroyo Seco 

 at Pasadena, California, June 29, 1910. 



The follomng records are from the west slope of the main Sierra 

 Chain: On the American River at Auburn, Placer County, California, 

 July 20, a single male was seen repeatedly at close range which had 

 probably strayed from one of the small spring-fed side streams. In 

 Bear Valley at Emigrant Gap, Placer County, Cahfornia, a single 

 male was taken July 21; two others were seen. This was at an ele- 

 vation of 4,000 feet, the highest elevation at which this species is 

 recorded, and is also the most eastern record, though it is still on the 

 west slope of the Sierras. 



Much that I shall write concerning Cordulegaster dorsalis wiU be 

 almost a repetition of that concerning Octogomphus, as the habits 

 and distribution of these in California are in many ways similar. 



As far as I have observed, C. dorsalis is found usually on those 

 swift mountain torrents which do not freeze in the winter time. 

 There may be exceptions to this, as I took this species at an eleva- 

 tion of 4,000 feet in Bear Valley (Emigrant Gap, Cahfornia), where 

 there is a heavy \\dnter snowfall and probably the streams freeze, 

 though many of them are fed by numerous springs which may 

 moderate their temperature. In the Coast Mountains of Cahfornia, 

 where it appears to reach its greatest numbers, it is found in the swift 

 upper reaches of all the perennial streams. Here it is associated 

 with Octogomphus specularis, AesJina walkeri,^ and Argia vivida, the 

 last breeding in the springs of the mountain gorges. I have never 

 seen or taken Cordulegaster, except in the steep canyons of the moun- 

 tains. It does not occur on the lower reaches of these same streams 

 after they have emerged onto the level valley floors and have lost their 



» See pages 588-592. 



