416 Transactions. — Zoology. 



" personal equation" of an observer. Plates XXIV., 1, and 

 XXIV., 2, of this paper are designed to show the details of 

 structure which may be taken as sufficiently constant through- 

 out the family, as far as the adults are concerned. 



The adults may therefore be said to be practically always 

 yellowish or tinged with red or brown; the wings carried flat 

 when at rest and not extending much beyond the abdomen ; 

 forewings usually rounded, pure white or spotted, patched or 

 banded with brown or red ; hindwings smaller, also rounded ; 

 vein in the forewing single, median, with one basal branch 

 {Aleurodes) , or a basal and a terminal branch (Ale^irodmis) ; 

 vein of hindwing single, median, with one basal branch''' ; 

 head small, transverse, oblique beneath, slightly convex above, 

 anteriorly rounded ; eyes two, red or brown, not prominent, 

 more or less reniform or sometimes divided, the anterior por- 

 tion the smallest ; a small simple circular ocellus close to 

 each eye ; antennae anterior to the eyes, consisting of seven 

 joints, of which the two first are short and simple, the rest 

 long, slender, and numerously ringed ; rostrum projecting 

 from the under-side of the head, composed of a single (?) 

 conical joint, at the apex of which are three tubular setae, 

 and from the base of which (beneath) springs a long sub- 

 cylindrical mentum, of three segments,! which is free in all 

 its length, and frequently extends beyond the thorax ; the tip 

 of the mentum is usually dark-coloured ; thorax short, the 

 pro-, meso-, and meta-thorax about equal ; abdomen mode- 

 rate, roundly tapering, terminated by the genitalia, and bear- 

 ing dorsally a minute tubercular organ]: (described more par- 

 ticularly below) consisting of an orifice, an operculum, and 

 a lingula ; genitalia usually dark-coloured ; genitalia of female 

 conical or subconical; genitalia of male forcipate; feet slender, 

 long, tarsi dimerous, terminal claws three, of which the 

 middle one is the shortest. 



The eggs, which are elliptical, pedunculated and usually 

 yellow or orange in colour, are produced in great numbers, 

 but seemingly only once in a year, although it would appear 

 (according to Eeaumur and Hegeer) that the period required 

 for hatching is ten days or a fortnight. 



The larva, as soon as it is hatched, fixes itself on the leaf> 

 and, as a rule, never afterwards moves from its position. In 



* Signoret thinks that perhaps there may be two or three " invisible " 

 veins in the forewing. 



t Westwood (Introd. to Mod. Class, of Ins., vol. ii., p. 442) says, 

 " promuscis 2-jointed " ; but it seems clear that he did not distinguish 

 the mentum. See his figure 118, 4. 



I Westwood (loc. cit.) says, " Abdomen neither tubercled nor corni- 

 culate"; surely an error. He likewise says of the feet — "ungues two," 

 but in his figure he shows three. 



