THE CANADIAN ENTOMOLOGIST 249 



There are two distinct groups. In the first, consisting of //. 

 tripimctata, H. liirldipennis, H. flavescens, II. lutea, H. fiisca, II. 

 rubromaculata, the nymphs are characterized by having the lamelhe 

 of the gills oblong, claws usually pectinated, distal segment of 

 maxillary palpus thickest about its middle and with a small tuft of 

 bristles near its distal end. The body is much flattened and the 

 colour olive brown or greenish yellow. The male imagos have the 

 penis lobes rather L-shaped and the second and third tarsal seg- 

 ments of the fore legs are equal, while the fourth is about four-fifths 

 the length of the second. In the other group, consisting of H. 

 canadensis, H. frontalis, and a third undetermined species represent- 

 ed by the nymph only, the nymphs have the lamella of the gills oval 

 and produced distally into a sharp point; the claws are not pectin- 

 ated, the distal segment of the maxillary palpus thickest towards 

 the distal end and the tuft of bristles larger than in group 1. The 

 body is less flattened, more reddish or yellowish, and has the ap- 

 pearance of being striped longitudinally on dorsal surface of abdo- 

 men. The male imagos have the penis lobes oblong instead of L- 

 shaped and the second and third tarsal segments are not quite 

 equal, while the fourth segment is about half the length of the 

 second . 



The following keys will serve to separate these eight species: 



Key to Male Imagos: 

 A. No black spots or bands on face below antennae. Group 1. 

 B. Very pale species. 



C. Notum ferruginous, stigmal dots 



distinct ^^- flavescens. 



CC. Notum lighter, no stigmal dots H. lutea. 



BB. Dark species. 



D. Large, entireh' brown species. 



E. Thorax with a broad dark median 

 stripe or two narrow stripes close 



together II  verticis. 



EE. Thorax without dark median 



stripe H- fnsca. 



DD. Not entirely brown. 



