THE CANADIAN ENTOMOLOGIST 43 



6 )PhaBlo pteryKHo<i 

 S)MaBlo9ratiaag^ ~>^ _7 jDexlldae 

 4 )H. 7Btrlolldae , ^ ,^»— "^ I SlSaroophaftldae 



3)EiorlstldB8^ ^<-^ / / "IjMa Kap roBopldae 



gjausoldaa ^ ^ — ' — \ / /  — ^lOJOeetrldae 



1 ) Phaslldae \ / y y ^. ^ IDCnterabrHae 



p r t ophaelldaeX -- T»ie PrlmeTal nmeoold etook with e long and wide faolal plata 



similar to that of the Muscid stem, but some stocks show a short- 

 tening of clypeus and inferior constriction of the facial plate, 

 foreshadowing and even approximating those of the extreme 

 types) . 



(9) Megaprosopid (10) Oestrid (11) Cuterebrid stem (Facial 

 plate reaches extreme of clypeal shortening and epistomal con- 

 striction). 



The lines of descent have not been simple, but on the con- 

 trary quite complex, and the plan merely indicates the general 

 trend in facial plate modification. From the Phasiid to the Oestrid 

 extremes the successively increasing difTerentiation may be traced 

 in successive types of ever greater clypeal shortening and epis- 

 tomal constriction. It seems almost certain that the facial plate 

 has specialized according to the retrogressive evolution here in- 

 dicated. There are several facts that appear to confirm this view 

 quite conclusively. Australia possesses no endemic oestrid nor 

 cuterebrid stock, but it has been the focus of a considerable number 

 of forms which must be considered as survivors of primitive phasiid 

 stock. These are Riitilia, Amphibolia, Microtropeza, Paramphi- 

 bolia, Amenta, Senostoma and Chrysopasta. Certain relatives of 

 these, also evidently to be classed as survivors of the same stock, 

 occur in the Australasian or Austromalaysian regions and streng- 

 then the case in hand. These are Paramenia of New Zealand, 

 Pseudoformosia of New Guinea, Stilhomyia of Java, and others. It 

 is to be noted that none of these, however, reaches either South 

 America or South Africa. Both of these continents were apparently 

 cut ofT from the Australian-Antarctic landmass at a time ante- 

 dating the greater or main dispersals of that branch of the primi- 

 tive phasiid stock which gave rise to these forms. These facts 



