196 MESOZOIC INSECTS OF QUEENSLAND, v.. 



Genus 8 t e r e o c h o r i s t a , ii. g. (Text-fig.23). 



Characters of the family, with the following additions : — 

 Forkings of Rs and M placed close together, at a level about 

 two-fifths from base of wing. Apical forkings of the branches 

 of Rs placed more than usually far distad. An oblique cross- 

 vein connecting Rs with M at a level just before that of the 

 origin of the posterior arculus. Branches of M intimately con- 

 nected by three cross-veins, which form three well-defined closed 

 cells distad from the median fork. 1A apparently three- 

 branched. 



Genotype, Stereochorista frustrate,, n.sp. ( Upper Triassic, 

 Ipswich, Q.). 



This genus would appear to be allied to Mesochorista (2, p. 29) 

 from the same horizon; but the remarkable characters of the 

 presence of a true posterior arculus and the shortened Ciii are 

 absolutely unique, and appear to warrant the formation of a new 

 family for its reception I do not know of any other Mecopteron 

 in which the posterior arculus can be definitely picked out; 

 either it is reduced to a transverse vein, not distinguishable from 

 a cross-vein, or else it is entirely obliterated by reason of the 

 complete fusion of Cu, with the main stem of M for a short dis- 

 tance. In this connection, it should be noted that, within the 

 single family Rhyaeophilidce in the Order Trichoptera, species 

 can be found showing all three conditions. Undoubtedly the 

 most archaic condition is that exhibited by Stereochorista, in 

 common with such species as Agape/us fuscipes Curtis (fam. 

 Rhyaeophilidce) and with the majority of the Alicrop/cryyidw, 

 viz., the presence of a true posterior arculus in the form of an 

 oblique vein connecting the main stem of M with Cu,, not far 

 distad from its origin at the cubital fork. The condition in 

 Stereochorista strongly suggests that the vein usually called Cu u 

 distad from pa, is in reality a fused vein consisting of Cuj and a 

 posterior branch of M, which we may call M 5 , and of which pa 

 is the basal free piece. If so, then the name posterior arculus, 

 due to Comstock, is a misnomer, and should be altered either 

 to anterior arculus (this being the part of the Odonate arculus 

 formed from M ) or simply to arculus. 



