54 NEW_ YORK STATE MUSEUM 



adhesion to the surfaces of the stones, fairly well developed in 

 Iron, very perfect in Rhithrogena. So complete is its 

 border that when applied to the surface of a stone, any elevation 

 of the abdomen would create a partial vacuum beneath it. It 

 doubtless serves in a different way the same purpose as the row 

 of smaller discsi possessed by the larva of the net-winged midge 

 (B lephar o cera), found in the same situations; and among 

 anatomical shifts for a living is one of the most remarkable 

 known to me. 



The three figures of mouth parts of nymphs of the four genera 

 hereinafter described (figs.12, 13 and 14) show very considerable 

 structural differences. It is because of the remarkable definite- 

 ness of such minute parts as the canines of the mandible that I 

 have been able to determine with certainty some of the elements 

 of the food of nymphs of Ohirotenetes albomani- 

 c a t u s , its food being all reduced to very minute fragments. 



Heptagenia interpunctata Say 



This is the commonest species in Fall creek at Ithaca, with 

 E. maculipennis a close second. Both species swarm into 

 trap lanterns set about the creek during July mostly subimagos 

 just risen from the water. During the daytime imagos are easily 

 found sitting on the vegetation along the sides of the gorge. 

 H. interpunctata is also a common species on the shore 

 of Lake Michigan near my home in Lake Forest, being very 

 abundant along shore in the latter part of August, associated 

 with H. flavipennis Walsh, and a few scattering speci- 

 mens may be taken as late as September. 



The rather well marked color pattern of the wing of this species 

 is shown in the photograph reproduced in Plate 4, fig.4. 



The nymphs of this species are found in all the streams about 

 Ithaca in rapid water under large stones. They are distinguish- 

 able at a glance from those of all other species by the black 

 markings of the under side, shown in pi. 6, fig.3. 



The nymph. (P1.6, fig.3). Length of full grown female nymph, 

 9.5 mm.; antenna, 2 mm., and setae, 11 mm. additional. 



Body strongly depressed, widest across the head, but with the 

 sides behind the head parallel to the middle of the abdomen, 

 thence tapering rather rapidly to the base of the setae. 



