30 Transactions. — Zoology. 



Male unknown. 



Hab. In Australia, on roots of Acacia longifolia : specimens 

 from Mr. French. 



This very large insect has much the appearance to the 

 naked eye of Coccus cacti (the cochineal insect), being of very 

 much the same size aiid colour ; but examination shows that 

 the characters just described are distinctly Acaiithococcid, 

 and, as no sign of a sac w^as observed on any of the specimens 

 sent to me, I have attached it to the genus Rhizococcus. In 

 this instance I think that the size of the insect may be taken 

 as a distinguishing character, being so much greater than that 

 of any other known species. 



Generic and Group Distinctions amongst the Acantho- 



COCCID^ AND THE DaCTYLOPID^. 



Plate IV., figs. 11-17. 



It is always useful to find some character which may at 

 once decide the position of an insect in a family, group, or 

 geiuis, and which will simplify the w'ork of the systematist. 

 Thus, for example, although in general appearance many 

 Aleurodids or Psyllids bear close resemblance to Coccids, 

 these latter may invariably be at once distinguished, whether 

 in the adult or larval stages, by the existence of only a single 

 claw on the foot ; and the observer may then with perfect 

 certainty proceed without further trouble as to the family. 

 So, again, the last abdominal segment in an adult female at 

 once decides its position amongst the Diaspids or the Lecanids. 

 I have thought that it might be useful to give here a guide to 

 a feature which wall mark, for a student of Coccids, a distinc- 

 tion between the AcantliococcidcE and the Dactylopiclo!. notice- 

 able almost at the first glance : I mean the form of the 

 antennal joints. In both subdivisions the number of the 

 joints may vary — the normal antenna of Eriococcus, for 

 example, has six joints, and that of Dactylopius eight joints, 

 but I believe I have not erred in attaching to these genera 

 such species as Eriococcus fagicorticis oy Dactylopius hibbertics, 

 which have seven joints. 13ut in almost all the species of 

 both with which I am acquainted there is this distinction : 

 that in the AcantliococciclcB the last joint is very little, if at 

 all, longer than the penultimate, whereas in the DactylopidoR 

 it is very considerably longer. I do not know of any excep- 

 tion to this rule as regards the former group ; but Dactylopius 

 eucalypti (presently described) departs from its type in having 

 a very short last joint, and is indeed abnormal in other re- 

 spects. The figures 11 and 13 of Plate IV. exhibit the 

 differences mentioned : it will be seen that there is a squatness 

 and "stumpy" appearance about the former, and a com- 



