58 



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

 margin of the abdomen. 



KEY TO THE NYMPHS OF DIASTATOMMA HEREIN DESCRIBED. 



Lateral spines on abdominal segments 7-9. 



Dorsal hooks distinct, narrowly prominent, ending in a pointed 

 tooth ; abdominal granulations fine and much less con- 

 spicuous than in the next species; male superior append- 

 age scarcely tubercled, lateral appendages three fourths 

 to four fifths as long. 1. severus. 



Dorsal hooks represented by a broad elevation, ending poste- 

 riorly on each segment in a rounded tooth; abdomen 

 evenly dotted with rather coarse blackish granulations; 

 superior appendage of male notched back of middle, in 

 front of which is a pair of tubercles, laterals about three 

 fifths as long as the superior one. 3. carolus. 



Lateral spines on abdominal segments 6-9; dorsal hooks as in 

 carolus but much more prominent; male superior append- 

 age scarcely tubercled, laterals nine tenths as long as 

 the superior. 4. sp. {a). 



1. Diastatomma severus Hagen. 



Ophiogoniphiis severus Hagen. 



The nymphs here described were collected by Dr. Forbes 

 in large numbers from streams in Yellowstone Park, such as 

 the Fire Hole River, Nez Perce Creek, and Gibbon and Good- 

 win rivers, during the latter half of August. They were found 

 on sand under stones in shallow rapids, and on weedy and 

 grassy bottoms. They answer well to the description given by 

 Hagen ('85, p. 259) for severus, which is by far the most abun- 

 dant gomphid in that region. 



The nymph, apparently grown, measures 25 mm.; the 

 abdomen, 16 mm.; hind femur, 5 mm.; width of abdomen 7 mm., 

 of head 5 mm. 



Color (alcoholic specimens) fulvous yellowish beneath and 

 on the sutures, and on the legs beyond the middle of the fem- 



