io Thomas Albert Williams 



Antennae reaching to rear of thorax, I and II pale, rest dusky; III 

 equaling IV and V together and rather longer than VI with its unguis, 

 cylindrical ; IV-VI club-shaped, III-VI irregularly and indistinctly annu- 

 late; VI with the contraction to the unguis abrupt. Wings delicate, the 

 three discoidals arising almost from the same place, the third subobsolete 

 at base. The apices of the first and second twice as far apart as those 

 of the second and third. Stigma rather broad. Legs dusky. Abdomen 

 yellowish green, pulverulent, the embryos showing very plainly. Length 

 of body 2.15 mm., to tip of wings 3.25 mm. ; alar expanse about 6.00 mm. 



On cottonwood. Lincoln, Weeping Water, Ashland, Squaw 

 Creek. One of our commonest aphids. It forms a gall at the 

 base of the leaves by causing the petiole to become twisted. The 

 winged insects escape through an oblique opening in the gall 

 where the edges of the twisted petiole come together. Winged 

 females are found in June. 



Specimens in collection of the U. S. National Museum (no. 

 124). 



7. Pemphigus populi-monilis Riley. 



Riley, Bull. U. S. Geol. Sur. Ter., Vol. V, I, p. 13, pi. II, fig. 3 (1879). 



Thomas, Ins. 111., 8th Rep., p. 205, fig. 45 (1879). 

 Winged female: Average expanse 6.50 mm. Black, the abdomen a little 

 lighter, especially at the tip, finely powdered with white ; broad across the 

 shoulders, the scutellar lobes of the mesonotum being rather more flat- 

 tened than the praescutum; the head rather small and narrow. Antennae 

 and legs rather short, the former reaching only to base of front wings; 

 6-jointed, I, II, IV and V subequal in length; III twice as long; VI not 

 quite as long as III; I and II very stout; III, IV and V somewhat cla- 

 vate, nearly smooth above, but with about 12 deep constrictions beneath. 

 Legs normal, with basal joints of tarsus tolerably well separated and 

 unguis stout. Wings subhyaline, front wings with stigma strongly angu- 

 late, dusky, the lower portion almost black. Veins dusky, the costal and 

 subcostal stout and darkest. The stigmal vein undulate, starting from a 

 little beyond the middle of the stigma. First and second discoidals almost 

 connected at base (in three specimens entirely so) and the distance be- 

 tween them about one third greater than that between the second and third 

 discoidals, and that between these two subequal with that between the 

 last mentioned and stigmal ; third discoidal obsolete at base, fold of hind 

 border but moderately thick. Hind wings ample, hook-angle but moderate, 

 the subcostal slightly undulate and considerably elbowed at basal third, 

 whence spring the discoidals, the first bending slightly toward posterior 

 margin, the second toward costal margin, the spaces between the tips of 



94 



