iVo.l.] EILEY AND MONELL ON APHIDID^E. 13 



stout but short promxiscis reacliing to liind coste ; ratlier large compound eyes. Pro- 

 j)ortions and shape of young PhijUoxera. 



True female: Legs short and the basal joint of tarsus rudimentary ; antenna? short, 

 four-jointed, smooth, joints subecpial, the third somewhat longest. Mouth rudiment- 

 ary. Described from skins surrounding impregnated egg. Males unknown. 



PEMPHIGUS POPULI-MONILIS, n. sp. 



[Gall (jwpiiU-moniUs) on the Narrow-leaved Cottonwood {Popiilus halsamifcra). A 

 series of more or less confluent moniliform swellings (Fig. 3, </) on the upi^cr side of the 

 leaf, each containing a single female, destined to become winged, Avhen it escapes from 

 btJneath, the winged insect -occuxiying the entire cavity of the gall. ] 



BIOLOGICAL. 



A very iuteresting gall, Avhicli may be called the Bead-like Cotton- 

 wood Gall, occurs on the Xarrow-leaved Cottonwood {Fopulus halsamifera, 

 L., var. angustifolia, Torrey), dnrmg the summer, in Colorado, and prob- 

 ably wherever this narrow-leaved variety grows. Though I have often 

 found the tree in cpiestion so covered with these galls, especially at 

 Greeley, that not a leaf was exempt, yet Populus monilifera, even when 

 growing along the bank of the same irrigating ditch and mingling its 

 branches with angustifolia^ would be entirely free from them. The galls 

 when not very numerous appear most commonly on the terminal leaves 

 of a twig. They form a confluent series of pale yellow ovoid swellings, 

 each side of the midrib (Fig. 3, g) recalling, in the distance, a lot of un- 

 lipe cherries, or, again, the galls produced on a true willow by the Saw- 

 fly larva — Kemcvtus salicis-pomum, Walsh. There will sometimes be three 

 rows of these swellings, and they are not infrequently tinted with red. 

 There are, however, more often but two rows, occupjdng nearly the whole 

 space each side of the midrib. The galls are formed by the folding-under 

 of the sides of the leaf and the bulging of the same around the insect, 

 which is always found solitary. The newly hatched louse is found in the 

 younger galls, and on the same branch, according to the age of the swell- 

 ing, the insect occurs in all stages of growth, the full-fledged female, with 

 her wings folded flat, fllling nearly the whole canity. After leaving the 

 gall, her wings are carried in the normal tectiform manner, and, when ren- 

 dered transparent by liquid, her abdomen is seen to be swollen with fifty 

 or more egg-like bodies, the dark eyes of which show conspicuously. These 

 bodies are the pseudova, and the female commences at once to deposit 

 them upon issuing from her dwelling. The yoimg, which free themselves 

 in the course of a few minutes from the confining pelhcle, are of a pale 

 yellowish-green, with black eyes. In structure, these young difler only 

 from the preceding generation, at a similar age, by the somewliat nar- 

 rowed body and by the promuscis reaching beyond the anus. J ust where 

 these young are deposited by the winged mother, I have not had oppor- 

 tunity to ascertain. They probably found new galls, the process coiitin- 

 uing until the late summer or autumn generation of winged females give 

 bkth to the sexual individuals, and these consign to the permanent 



