BY R. J. TILLYARD. 



•209 



veinlets in the former, even in the short space of the wing pre- 

 served in the fossil. This character might be passed over as of 

 little importance, were it not quite incompatible with the funda- 

 mental character of the family Psychopsidce, viz., the broadly 

 rounded apex, with wide costal area from base to tip. Those 

 Liassic and Jurassic Prohemerobiidce which are best preserved 



Text-fig. 2X. 

 Megwpyschops illidyei (Froggatt). Basal third of forewing (a) and hind- 

 wing (//) for comparison with Text-fig.27; ( x 5). 



show, for the most part, a costal area fairly broad at the base, 

 but rapidly narrowing towards the apex, which is always much 

 less rounded than that of the Psyckopsidce] concurrently with 

 this more primitive shape, there is an entire absence of any 

 formation of a vena triplica, the three veins Sc, R n and Rs 

 remaining primitive in form from base to apex. Now, if we 

 turn to the study of the wings of any Psychopsid, we see that 

 the broad apex, together with the specialisation of the greater 

 parts of Sc, Rj, and Rs as a vena triplica, is correlated with a 

 condition of the costal veinlets which is quite different from that 

 found in the fossil. In the Psyckopsidce, these veinlets, from 

 near the base right up to near the end of the vena triplica, come 



