128 BRITISH APHIDES. 



to be that of Kessler and Low. That genus necessi- 

 tates the presence of one single obhque vein in the 

 lower wing. All the specimens I possess show two 

 oblique veins, which I look upon as constant. 



M. Derbes, in 1868, described an insect which feeds 

 on Pistacio terehinthmn^ to which he gave the name 

 PemjyJiigus pallidus, but this manifestly is quite a 

 different species from this on the elm tree.* 



As Haliday publislied his researches in 1839, priority 

 should be given to the name he gave his insect, and 

 accordingly I retain it, 



Haliday's description of Eriosoma iDallida is as 

 follows : — " It inhabits the mountain-elm. Its follicles 

 are more solid and embedded in the leaves, near the 

 base of the midrib, not elevated on a foot-stalk, .... 

 than in Eriosoma ulmi gallarimi. The apterous female 

 of E. ijallida is white. The follicles burst about the 

 beginning of August. ■ The society then is very 

 numerous, and the farinose secretion more abundant 

 than in that species." He then describes the winged 

 form and says, "the nerves of the upper wingare nearly 

 as in E. ulmi gaUarum [Tetraneuraulmi), but the lower 

 have two nervures (in the place of one) springing 

 from the sub-costal. The joints of the antennae also 

 are of different proportion, the sixth being rather 

 longer than the fifth. "t 



Pemphigus filagints, Fonsc, Pass. Plate CXIV, figs. 



1—4. 



Aphis filaginis, Boyer de Fonsc. 

 Pemjpliigus gnaphalii^ Kalt., AYalk., Hardy. 



Apterous viviparous female. 



Inch. Millimetres. 



Size 0-080X0-050 2-02xl-27. 



* M. Liditenstein proposes, in a letter to me, that, to avoid confusion, 

 this insect should in future be called Pemphigiis Derbesi. 

 t A. H. Haliday, ' Ann. Nat. Hist.,' vol. ii, p. 189. 



