AQUATIC INSECTS IN NEW YORK STATE 265 



■quired an unusually careful examination of the nymphs of the 



two species to detect any differences whatever. I find only the 



following, and am not assured as to how constant these will 



prove. C] The front border of the median lobe of the labium in 



externus is slightly but distinctly convex [see Bui. 47, pi. 20, 



fig.l2] ; in f r a t e r n u s it is straight or scarcely convex. 



This is probably a good character. (2) The lateral spines of the 



ninth abdominal segment are something more than two times 



the length of the tenth segment in extern us; in frater- 



nxLB they are something less than two times the length of the 



tenth segment. 



Gomphus borealis 



I now regard this as a species, and not a variety of G. d e - 

 Bcriptus. I described it as a variety because I was unable 

 to give any satisfactory character for the separation of females; 

 but a more careful examination of my specimens reveals differ- 

 ences in the form of the hind margin of the occiput, that appear 

 to be reliable. In the female of b o r e a 1 i s the occipital mar- 

 gin viewed from the front exhibits two low, rounded lobes, be- 

 tween which is a depression whose curvature is exactly the re- 

 verse of the convexity of the lobes. In the female of d e s o r i p - 

 t u s the occipital margin is scarcely bilobed, and the median 

 half of it is straight, not concave in the center at least. Com- 

 paring the nymphs again, descriptus nymphs from Ithaca 

 with borealis nymphs from Saranac Inn, I find that the 

 lateral spines of the sixth abdominal segment in borealis 

 are half as long as those of the seventh segment; in descrip- 

 tus, about equal in length on these segments. 



GOMPHURUS 



This subgeneric name I have used as a convenient designation 

 for the d i 1 a t a t u s group of Selys. Mr Williamson has in- 

 eluded some of its species in Stylurus^, but I prefer as yet to 

 restrict that name to the very homogeneous group of species 

 whose separateness was indicated by Hagen in the Transactions 



I — — ■■ — ~ ■ 



lAmer. Ent. Soc. Trans. 27:205-17. 



