PLECOPTERA OF NORTH AMERICA 69 



Key to the Species. 



Males. 



Lateral stylets of supra-anal process not reaching 

 its cap frontalis 



Lateral stylets of supra-anal process just reach- 

 ing its cap elongatus 



Lateral stylets of supra-anal process surpassing 

 base of its cap colubrinus 



Females. 



Subgenital plate deeply and widely cleft— frontalis 

 Subgenital plate shallowly notched at its tip 



elongatus 



Subgenital plate narrowly and deeply cleft 



colubrinus 



Isogenus frontalis Newman. 



(Plate 10, figs. 10, 13, 14, 15, 16; plate 11, fig. 1.) 



1838. Isogenus frontalis Newm., Ent. Mag., 5:178. 



1841. Nephelion frontalis Pict., Hist. Nat. Perlides, p. 172. 



1861. Isogenus frontalis Hagen, Syn. Neur., N. A., p. 18. 



1883. Pcrla sulcata Prov. Pet. Faun. Can., Neur., p. 74. 



1918. Perla titusi Banks, Bull. Mus. Comp. Zool., 42:6. 



1920. Perla incesta Banks, Bull. Mus. Comp. Zool., 64:318. 



Length to wing tips, male, 18-24 mm.; female, 20-25 

 mm. Expanse of wings, male, 30-35 mm. ; female, 36-42 

 mm. 



Color brown to blackish, with a yellow stripe on the 

 prothorax, and a large yellow triangular spot on the rear 

 of the head. Head blackish above except for this spot 

 (whose apex reaches forward to the suture behind the 

 ocelli), and a pair of divaricate yellow dashes, that border 

 the arms of the obscure transverse blackish frontal M- 

 mark in front. Edge of mouth above and head beneath 

 pale. Antennae and palpi brownish, the latter darker. 

 Ocelli minute, the laterals half as far from the eyes as 

 from each other. 



Prothorax rectangular, about one fourth wider than 

 long: its middle yellow line is divided by a sharp brown- 

 ish longitudinal sulcus. The sides of the disc are densely 

 covered with rather coarse blackish marmorate markings. 

 The mesothorax is yellow before the wing roots, and dif- 

 fusely so along the middorsal line. Legs brownish with 



