548 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



VOL. 52. 



dominal spines are very variable in length, some being short and blimt, 

 others unusually long. Such variations occur even on the individual. 

 In one the spines on segment 6 are blunt, on segments 7-9 long and 

 pointed. 



OPHIOGOMPHUS SEVERUS Hagen, nymph. 



A medium colored nymph, only moderately hairy; 26-29 labial 

 teeth. Abdomen with dorsal hooks on segments 2-9, low and weak. 



244 



I'lGS. 239-243.— OPHIOGOMPHUS, DORS.^L 8riNES OF NVMrilS. 239. U. BISON. 240. O. OCCIDENTIS. 241 

 O. MOERISONI. 242. O. MORRISON! NEVADENSIS. 243. O. SEVERUS. 



Figs. 244-246.— Ophiogomphus, lateral fringe on segment 7 of nymph. 244. O. morrisoni neva- 



DENSIS. 245. O. SEVERUS. 246. O. MORRISONI. 



Lateral hooks on segments 7-9. The paired superior appendages 

 four-fifths as long as the median appendage. (See figs. 220, 230-232, 

 243 and 245.) 



Length, 28 mm.; abdomen, 19; hind femur, 4.75; width of ab- 

 domen, 8. 



Described from exuviae collected on Satus Creek, Yakima Comity, 

 Washington. I have specimens of this taken emerging. 



OPHIOGOMPHUS MOKRISONI Selys. nymph. 



A medium to dark nymph, very hairy; each abdominal segment 

 on its dorsal aspect fringed posteriorly with nimierous long hairs; 

 25-29 labial teeth. Abdomen with dorsal hooks on segments 2-9, 

 these longer and more erect and more slender than in other species, 



