439 



Syxopsis of Gexeka. 



A^ Forewings not opaque; vertex not })n)cliu'C(l into processes 

 in front. 



R^ Hind til>iae witliont basal spnrs. 



CJ. Forewinii' Avith tliree narrow black S])ots on hiixl mar- 

 gin, one in eaeli marginal cell and a third Ijetween 

 tlieni ; veins Avithont prominent setae. 



D\ Gcnal cones present Trioza Foerster 



D-. Genal cones wanting Kuirayama Crawford 



C". Forewing witliont marginal spots ; veins with promi- 

 nent setae Hcraheva Kirkaldy 



B-. Hind til)iae with l)asal spnr and snhapical spine.... 



.-Mcfjafrioza Crawford 



A-. Forewings opaqne or nearly so ; vertex prodnced in front 



into two protnberances above genae 



Cerotrioza C^'awford 



Genns Tkioza Foerster. 



This genns has representatives in praeticallv all countries 

 wdiere Psvllidae occnr. There are five closely related endemic 

 species in this archipelago, so far as known all living on the 

 foliage of ohia lehna (Mctrosideros spp.). It seems cpiite cer- 

 tain that all are derivatives of a common ancestor which estal)- 

 lished itself here long ago, coming probably from some land 

 area in the sonth Pacific. Living species resenil)ling these in 

 essential characters and certainly allied to them are known in 

 Polynesia, Australia and Sonth America, bnt it is not possible 

 yet to make a more definite statement of the ancestry of these 

 species. 



The ancestral species has apparently divided by variation 

 in the following manner: Trioza iolanl and oliiacola are prol)- 

 ahly concurrent derivatives from the original species on the 



