38 NEW YORK STATE MUSEUM 



cultriform galeae, fringed with spinules externally, and broadly 

 triangular laciniae, separate to the base. 



Prothorax rather short, closely applied to the front of the large 

 mesothorax ; wing cases reaching the apex of the second abdominal 

 segment. Legs rather short, stout, pale, with darker lines upon 

 the sutures, the darkest one at the base of the claw. 



Abdomen gradually tapering, gracefully upcurving in the rear. 

 Gill laminae on segments 1-7, similar in form on all the seg- 

 ments (fig.6) ; smallest on segment 1, largest on segment 6, obo- 

 vate, with a somewhat thickened front margin, and a longitudinal 

 dorsal chitinous ridge. There are no free gill filaments attached to 

 lamellae. Lateral spines on segments 4-9 straight, sharp, increas- 

 ing in size posteriorly. Setae rather short and stout, equal, 

 fringed copiously within, traversed by a broad distinct band of 

 brown which occupies their middle third, and slightly washed 

 with brown again at the extreme tips. 



This nymph differs from the one figured by Eaton (pl.49, 

 Monograph) in having the middle lobe of the tongue (hypop- 

 harynx) bilobed. This genus differs from all others as; yet 

 known except Thnaulus in the possession of a pectinated 

 fringe on the distal border of the galea of the maxilla. 



Choroterpes basalis Banks 



This species I have studied in the Fall creek gorge beside the 

 Cornell Insectary at Ithaca. It is a very common species there. 

 The nymph is found among the smaller stones in the side cur- 

 rents of the creek in the bottom of the gorge, associated with 

 other nymphs ofEcdyurus maculipennis, Baetis, 

 a e n i a etc. It clambers about under these stone's, and when 

 they are lifted out of the water it is easily picked off by hand. 

 The form of the gill tips (Plate 8, fig.8) will instantly distinguish 

 it from all others in the stream. 



Imagos were abundant about the middle of July. My bred 

 specimens are dated July 14, 1901. Not many imagos were ob- 

 served at large except on early afternoons,, when the sunshine 

 was warm and bright. Then they would swarm out in the open- 

 ing of the gorge, and dance high up in the air between the banks 

 of green in myriads. Rising and falling in rapid undulations, 

 moving in large companies up and down the gorge, they rarely 

 descended low enough to bring the lowermost within the reach 



