256 AUSTRALIAN PSYLLIUM, 



between the larva and pupa, or where one stage ends and the 

 next commences. In dealing with their development, when all 

 stages have been obtainable, I have taken the smallest form to be 

 found as the larva, and defined the pupa from the largest, 

 frequently just as it is ready to cast its skin and emerge as the 

 perfect insect. Though the changes are gradual, each moult brings 

 some alteration; first, the abdominal segments show the line of 

 separation from the thorax, next the line between the base of the 

 head and thorax, and the enlargement of the wing-covers. The 

 antenna?, though not increasing much in length, show more joints; 

 in the earlier stages the 3rd joint is very long, and the additional 

 joints, until the normal number of nine is reached, appear to 

 divide off from the apical portion of the elongated third joint, 

 which, however, is generally the longest in the perfect Psylla. 

 Many of the larva? and pupa? are covered with fine hairs; most of 

 the species that are naked (not forming lerps or galls) have the 

 hairs upon the dorsal surface covered with tiny particles of white 

 sugary secretion, with those on the sides converted into white 

 filaments sometimes of considerable length. 



The perfect insect might be compared to a minute cicada in 

 general form, but there the actual resemblance ends. The head 

 is generally broader than long, sometimes deflected, with large 

 eyes; the ocelli three in number, the lateral ones placed on the 

 summit of the head close to the hindmargin of the eyes, and the 

 central one at the lower margin at the apex of the median suture. 

 The face lobes are generally hairy, sometimes long and projecting 

 in front of the head; in some species angular, rounded, short or 

 ribbon-shaped and almost hidden; or exceptionally wanting in 

 some groups; the form of the processes seems to be of consider- 

 able generic value. The antennae are composed of ten joints, the 

 first two shorter and thicker than the remaining generally filiform 

 ones, and terminating at the apex with two short seta?. 



The thorax is broad, the pronotum narrow, with the mesonotum 

 divided into three unequal parts — the first the dorsulum, the 

 second the mesonotum proper, large and broad, and the third or 



