310 
tions both of American and foreign aphids at my command, I have 
arrived at the conclusion that the species infesting so disastrously the 
various kinds of cucurbitaceous plants is identically the same as Aphis 
gossypii Glover, and that the descriptions of Aphis citrifolii Ashm. in 
part; A. citrulli Ashm.-, A. cucumeris Forbes, and probably A. forbesi 
Weed, are referable to the same species. I am also of the opinion that 
part of the description of A. rumicis, by Prof. 0. Thomas, may be 
referred to it. 
Whether or not any of the described European species are identical 
with it, I am at present unable to decide, since none of the descriptions 
fit our American insect exactly. 
From the very large quantity of material at my command, I have 
been enabled to observe extreme variability of coloration both in adults 
and larvse, whether on the same or different plants, whereas all the 
important structural characters remain the same in all. 
The darkest of its apterous forms, and also the pupae, bear a great 
general resemblance to A. rumicis, which, however, is a considerably 
larger and more robust insect, having longer and stouter antennae and 
larger nectaries, while the antennal sensoria are more numerous and 
more irregularly arranged tnan in this species. 
The first account of this plant-louse was published by Prof. Townend 
Glover in the Patent Office Eeport for 1854, p. 62, with figures on 
Plate 3, which article was reproduced in the Patent Office Report for 
1855, p. 68, Plate vi, Fig. 2, though the specific name was first applied 
in the Report of the Department of Agriculture for 1876, p. 36, Fig. 39. 
Professor Glover's account of this plant-louse is in substance as 
follows : 
When the cotton plant is very young and tender, it is particularly subject to the 
attacks of the cotton louse, and the constant puncturing and drainage of sap from 
the young leaves enfeeble the plants to such a degree that the leaves are caused to 
curl, turn yellow, and subsequently wither away and fall to the ground ; and although 
young plants are most subject to these attacks, he has seen old stands of cotton in 
Georgia with their young shoots completely covered with this pest as late as 
November. 
In 1880 Mr. Wm. H. Ashmead redescribed this species in his pam- 
phlet on " Orange Insects," under the name of Siphonophora citrifolii, 
which he found to be infesting his orange trees, without being aware 
that the same insect infests also cotton and had been described pre- 
viously. 
Again in 1882, Mr. Ashmead, in a paper on the "Aphididae of Flor- 
ida" in the Canadian Entomologist (vol. xiv, p. 91), in discussing 
dimorphism among insects, besides reproducing his original descrip- 
tion, makes the serious mistake of describing on page 92 another species 
as a dimorphic form of his citrifolii, which, however, according to the 
characters given in this description, is neither a true Aphis nor a 
Siphonophora, but appears to belong to the genus Rhopalosiphum. 
Mixed colonies of closely related and other species of aphides are fre- 
