544 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 52. 



Abdomen, male, 35.5 mm.; female, 37.5-38; hind wing, male, 28 

 mm.; female, 30.5-32. (Structural details, figs. 213-218.) 



I have a male taken on the Sacramento River at Colusa, a male 

 from the American River at Sacramento City, and three females 

 from the American River at Auburn. In structure these are un- 

 doubtedly occidentis, but in color they are very much lighter than 

 the occidentis of Umatilla and Satus Creeks in the Columbia Valley. 



The Colusa male was taken June 11, while the other male was 

 caught July 15, 1914, in the willow thicket across the American River 

 from the city of Sacramento and was the only Ophiogomphus seen 

 at this point. The three females were caught July 19, 1914, among 

 the rocks below the dam in the American River Canyon at Auburn, 

 California, where only one other specimen was seen. 



11. THE NYMPHS OF OPHIOGOMPHUS. 



The following generic characterization of the OpJiiogonvplms nymph 

 is given by Needham in The Dragon Flies of Illinois:* 



Nymph stout, little flattened. Head abruptly sloping forward from the ocelli. 

 Labrimi pilot-shaped. Antennae with the two basal segments globular, tliird segment 

 twice as long as both basal, much flattened and laid close beside the labrum. Fourth 

 joint a minute rudiment. Median lobe of mentum rounded, with border of short 

 blunt teeth and a double series of fringing scales. Lateral lobes nearly straight, not 

 terminating in an end hook and minutely denticvdated within; movable hook short, 

 arcuate. 



Legs rather short. Fore and middle tibiae Avith external hooks, wing-cases divari- 

 cate, strongly sloping downward toward the sides. Dorsal hooks on abdominal 

 segments on 2 or 3-9. Tenth segment not inclosed by the 9th but triquetral, 

 exceeding the lateral spines, its own lateral margin forming a part of the margin of 

 the abdomen.- 



The nymphs of the western species of this genus are separated from 

 one another with considerable difficulty. Figures 224, 227, 230, 233 

 and 236 show labia of the five species, which, as with any other single 

 character of the nymphs, vary too little to be of any use in separating 

 the species. The dorsal spines are also practically the same in aU 

 species. The characters used in the following notes are the only ones 

 I have found to be of value. 



KEY TO NYMPH.S. 



a}. Segments 6-9 with lateral spines. 



6'. Superior appendages three-fourths length of median appendage; dorsal hooks 



strong hison. 



¥. Superior appendages two-thirds length of median appendage; dorsal hooks heavy 



but low, only those on segments 2-4 erect occidentis and o. calif ornicus. 



a?. Segments 7-9 with lateral spines. 



c^ Dorsal spines weak and low, only the first two or three erect severus. 



c^. Dorsal spines slender, erect, well developed morrisoni and m. nevadensis. 



iBull. 111. State Lab. Nat. Hist., vol. 6, art. 1, 1901, p. 57. 



= The nymphs of Erpetogomphus are distinguished by dorsal spines on segments 2-4 only. I have exam- 

 ined nymphs of compositus, designatus, and an undescribed species. 



