HEMIPTERA. 165 



Three genera occur in this country. These can be distinguished 

 as follows: 



A. Hind wings with two discoidal veins. i. PEMPHIGUS. 

 A A Hind wings with only one discoidal vein. 



B. Antennae six-jointed. 2. Ti IK \NKURA. 



BB. Antennae five-jointed. 3. HORMAPHIS. 



Among the common representatives of this section are certain 

 species of Pemphigus^ which make galls upon various trees of the 

 genus l\*pulus. One of these, the Poplar-leaf Gall-louse, Pemphi- 

 gus populicaulis, is common on the leaves of cotton-wood and of 

 aspen. It makes a swelling the size of a small marble on the leaf at 

 the junction of the petiole with the blade. This gall is of a reddish 

 tint, and has on one side a slit-like opening. In the early part of 

 the season each gall is occupied by a single, wingless female, prob- 

 ably the agamic stem-mother, which, by midsummer, becomes the 

 mother of numerous progeny; these often amount to one hundred 

 and fifty in number. 



A closely allied species occurs throughout the Western and South- 

 western States, which makes a similar gall near the base of the leaf 

 of Populus monolifera and P. balsamifera. This gall has a trans- 

 verse slit-like opening, which probably suggested the name of the 



*hlgus populi-transvcrsus. As in the preceding spec 

 the gall is started in the spring by a single, wingless stem-mother; 

 by the latter part of June the stem mother is surrounded with young 

 of various sizes, all covered with the usual white secretion, and 

 mixed with liquid globules. A generation of winged individuals is 

 produced in the autumn, sometimes not until the leaves have fallen. 



Another of these species is known as the Vagabond Gall-l- 



htindus. It infests the tips of the twig ' .iin 



cotton-woods and the balsam poplar: here- it m.i' -rugated 



galls, which somewhat resemble the flower of the double cockscomb 

 of our gardens. Ti '.Is turn black, and remain on the t 



dur; On opening tin- galls in midwinter I have found 



'many of win- in them. 



Section II. Smi/< >\i IKI 

 This section includes genera in whuh tin third discoidal vein of 



front wings is forked ; the .mt nn.r .<. 



