THE CANADIAN ENTOMOLOGIST. 15 



The opinion which, for many years past, I have persistently advo- 

 cated, as regards the study of Coccidaa, is that it is always better to base 

 distinctions, where possible, upon anatomical characters of the insects 

 themselves, rather than upon external features of the coverings, waxy or 

 cottony, or otherwise, under which they are sheltered. These coverings 

 may vary so much according to accidental circumstances that I think they 

 should be considered as of secondary, or even less, importance. In the 

 case of the two insects of which I am now treating, I am sorry to say 

 that I did not adhere strictly enough to my own rule. Size, colour, form 

 of the scale, food-plant, and such like things, have been so greatly insisted 

 upon, as I find, in all the accounts of Aspidiotus perniciosus, that I 

 have perhaps attached too much importance to them, and, consequently, 

 it is possible that my identification of Agnidia fusca is erroneous. 



All the authors who describe Asp. perniciosus give the following 

 characters of it : — 



1. The scale is "gray" ; the pellicles "yellow or reddish-yellow," "some- 



limes black." 



2. When on twigs, " the wood beneath the bark is stained red"; "the 



cambium layer of wood is stained purplish " ; the " peculiar red- 

 dening effect on the skin is a very characteristic feature " ; " the 

 cambium layer frequently becomes deep red or purplish" ; "if the 

 twig be scraped with the finger-nail, a yellowish oily liquid will 

 appear." 



3. The diameter of the female puparium, or scale, is given by Comstock 



as about one 13th inch. I do not find it in other writers. 



4. The principal food-plant, as mentioned above, is the pear ; when the 



peach is mentioned it is only incidentally, or as very slightly 

 attacked. 



5. No mention is made by authors of the second female pellicle as being 



any larger than the adult female. 



Now, in all the foregoing characters, the specimens on which I 

 founded my Agnidia fusca differ from Asp. perniciosus; and if one 

 might accept as positively final the statement in " Insect Live " (Vol. 

 VIII., p. 289), that "the Sart Jose scale differs from all others in the 

 peculiar reddening effect which it produces," then there would be no more 

 to be said ; for Agnidia fusca produces, as far as I know, no such 

 effect. In size, A. fusca is much smaller, the female puparium having a 

 diameter of one 35th inch. In colour it is " very dark brown or dull black ; 



