326 CONNECTICUT GEOL. AND NAT. HIST. SURVEY. [Bull. 



Pemphigus Hartig. 



Antennae of stem mother four- jointed. Wax pore plates not 

 developed on head ; present on thorax and abdomen. Prothorax 

 with four plates in a transverse row. Young of stem mother 

 acquire wings ; third generation apterous. Alate viviparous 

 females with six-jointed antennae. Mesothorax of fundatrigeniae 

 usually without wax pore plates. Sexuparae always with such 

 wax pore plates. 



Fore wing with M simple. Hind wing with media and cubitus 

 well developed. Cornicles normally wanting. Rudimentary 

 gonopophyses, three. Sexuals small, beakless, females laying but 

 one tgg. Antennae four- jointed. Stem mother and second 

 generation only occupying galls. Gall production is highly devel- 

 oped in this genus. The species produce galls on the leaves, leaf 

 petioles and young wood of the winter host. Summer generations 

 live on the roots of grasses and herbs. One species only produces 

 aerial colonies on the summer host. 



The characters available for the determination of the species of 

 this genus are so variable and several of the species are apparently 

 so closely related that their separation is extremely difficult. Certain 

 relative proportions appear to hold and serve as a means of 

 separating these closely related species. 



These relative proportions are what the writer terms the 

 coefficient of antennal joint vi determined by the following 

 formula : 



Length of vi + spur 



length cf iii 

 and the antennal coefficient which is found as follows : 

 Length of iii -f- iv -j- v + vi -f spur 



length of hind tibia 



These coefficients are used in the following key. The species 

 P. populivenae is placed in the key tentatively. In certain collec- 

 tions made the writer finds a species which produces galls such as 

 Fitch describes for P. populivenae. This material combines the 

 characters of both P. populicaulis and P. populiglobuli. Further 

 study is needed to determine the validity of this species. 



Key to Species. 



1. Greatest diameter of joint iv of antennae not distinctly less than 



that of v 2 



Greatest diameter of joint iv of antennae distinctly less than that 

 of v. A large, irregular-shaped sensorium on distal one-half of 

 v and vi. Normally the membrane of these sensoria bear small 

 islands of chitin, each bearing one to several hairs populi-transversus 



(Fundatrigenia) 



