320 FOREST ENTOMOLOGY. 



The insects are smaller than those in the preceding species, and 

 differ in a few minor specific points. 



Pemphigus pallidus (Haliday). 



In fig. 296 an illustration is given of P. pallidus, which forms galls 

 on the midrib of wych elm. The specimen from which the photo- 



Fig. 295. " Corkscrew " gall on Pig. 296. Gall of Pemphigus pallidus on midrib 



leaf -stalk of poplar caused by of leaf of wych elm. 



Pemphigus spirothec. 



graph was taken was found in High Legh, Cheshire, where it was 

 very common. 



The fully developed insect is somewhat variable in size. Thediead 

 and thorax are black ; abdomen yellow ; eyes red ; antennas darkish- 

 brown. 



Tetraneura ulmi (De Geer). 



Closely allied to the Pemphigus, and belonging to the same tribe, is 

 the genus Tetraneura, with a single species, Tetraneura ulmi. 



The galls of this species are found on the upper side of elm leaves 

 (fig. 297) about the middle of May. They are nearly one-fourth of 

 an inch in length. I have frequently found the galls projecting from 

 the folded portion of the leaves injured by Schizoneura ulmi. Thus 

 we get two species very closely allied entomologically, and practically 

 united botanically. The entrance to the galls of Tetraneura is well 

 closed, and guarded by hairs which doubtless act as a protection 

 against parasites. 



