44 



The labium extends posteriorly beyond the bases of the 

 second pair of legs. The median lobe is considerably produced, 

 and rather deeply cleft in the middle, the angles each side of 

 the cleft minutely rounded. Lateral lobe squarely truncate on 

 the end, with a minute tooth terminating the inner border, 

 which is finely denticulate. Movable hook long and arcuate. 

 Supracoxal processes of equal length, a little obtuse, pointing 

 in slightly diverging directions, the angle between them about 

 75 degrees, the posterior a little broader. 



Abdomen with lateral spines on segments 5 to 9, increasing 

 in length posteriorly, those of 5 very minute and rudimentary, 

 of 6 somewhat appressed, of 8 and 9 nearly equal, of 9 three 

 fourths as long as the 10th segment at middle. Appendages 

 longer than segments 9 and 10, inferiors longest, slightly in- 

 curved at tip ; superior four fifths as long as inferiors, exactly 

 intermediate in length between the two pairs, a pair of short 

 spines at its terminal angles, between which the tip is semicir- 

 cularly notched, sides parallel and fringed with fine hairs, its 

 basal male enlargement elongate, triangular, scale-like, cover- 

 ing its basal three sevenths ; laterals three fourths as long as 

 superior, cylindrical, abruptly acuminate apically. 



3. J^schna sp. {a). 



A number of small nymphs from Yellowstone Park and 

 Montana, 15 mm. and less in length, appear to be different 

 from any others known to us. The lateral spine on the sixth 

 segment is very small ; on the fifth segment there is merely a 

 smooth angulation ; the rear angles of the head are very slightly 

 or not at all rounded. The supracoxal processes are exactly 

 equal and similar. The very young individuals (7.5 mm.) are 

 not transversely banded. The nymphs are too young for any 

 comparison of the lengths of the terminal appendages. They 

 were collected July 25 to August 19 from bark and rotten logs 

 in a bayou of Flathead River, near Demersville, Montana, and 

 in Yellowstone Park from the Gibbon River and a lagoon of 

 geyser water near Lewis Lake. 



