244 



BUIyl/ETIN OF THE BUREAU OF FISHERIES. 



The Nymph. — Like the egg from which it was hatched, the nymph is a little larger than any of the 

 others here included, being 1.25 mm, long and 0.42 mm. in diameter. Its general color is white, the eyes 

 and the center of the abdomen reddish brown, the respiratory system bright yellow. There are two com- 

 paratively large horns on the dorsal surface of the head at the posterior margin, with their tips turned back 

 like hooks; that is, they are slightly " cultriform ' ' (Needham). The inferior posterior appendages of the 

 tenth abdomen segment are large and are turned over vertically at right angles to the body axis. The 



Figs. 55 to 57. — Development of Epicordulia princeps: 55, egg; 56, mask of newly hatched nymph; 57, newly hatched nymph. 



antennae are banded with black and white in sharp contrast; the base with a narrow, white, distal band; 

 the basal half of the first joint black, the distal half white; the second joint the same, the third joint 

 entirely white. The legs are transparent, with very little differentiation in color, the tips of the basal 

 joint, the femur, and the tibia being somewhat whiter than the rest of the joint. The thorax is pale white, 

 without any pigment; the abdomen is brownish red through the center over the intestine, with short, 

 dark spots on the posterior margin at the outer edge of each segment, the rest white. 



The Mask. — Mentum three-fifths wider than long, its sides slightly concave, the distal margin a 

 little less than twice the proximal; one lateral seta, two marginal setse on either side; three mental setae 

 on each half in a straight line, the distal one nearest the midline; four stout, sharp spines at the center 

 of the distal margin. Lateral lobes about the same length and width ; two setae on the outer border, none 

 on the blade of the lobe ; raptorial seta reaching beyond the tip of the movable hook, the latter short 

 and stout; distal margin with 10 teeth covering its entire width, the outer 5 much larger than the inner 

 5 and cultriform. Lateral seta on mentum often lacking as in figure 56. 



The eggs were laid in the leaves of crex grass; more than a thousand were obtained from five grass 

 leaves July 26, 191 7. These began to hatch in two weeks and continued hatching for 10 days, but, like 

 the eggs of Epicordulia, there was no way to determine just when they were laid, so that the period of 

 incubation is uncertain. 



The Egg. — These eggs were in the form of an elongated ellipsoid, the long diameter four times the 

 shorter one, the anterior end broadly and bluntly rounded, the posterior end pointed; neck short and 

 broad and brown in color. 



The Nymph. — The head is transversely elliptical in outline, the two diameters in the ratio of 8 

 to 5; there is a pair of setae just inside of each eye on the dorsal surface, another pair close to the mid- 

 line, just behind the anterior margin, and a single seta at the center of the margin itself. The thorax 

 is considerably narrower, but almost twice as long as the head ; the legs are long and stout, the posterior 

 pair reaching somewhat beyond the center of the caudal gills. The abdomen is a little wider than the 

 thorax anteriorly and does not narrow much in front of the seventh segment. The antennae are long 

 and stout, with a gray band at the base of each joint; caudal gills as long as the rest of the body and 



ENALLAGMA HAGENI. 



