BY R. J. TILLYARD. 613 



very delicate wings, it is impossible to say definitely whether 

 these veins are specialised oblique cross-veins, or really descend- 

 ing branches of Ciij which fuse with Cu 2 . Their evident 

 strength would incline one to the latter belief. But the decision 

 must stand over for the present; and I will content myself with 

 calling attention to their existence, without taking them into 

 consideration at all in the construction of the Archetype of the 

 Complex. If further discoveries should prove that they are 

 true branches of Cu 1( then it is clear that that vein must origin- 

 ally have had more branches than we at present suppose; and 

 the Archetype of the Complex must be altered accordingly. 



The Archetype of the Paratrichoptera clearly agrees with the 

 usual definition of the venation of the Order Mecoptera in many 

 points. It seems inevitable that, sooner or later, the discovery 

 of intermediate forms, either in the Permian or Trias, must link 

 the two together, and cause us to merge the Order Paratrichop- 

 tera into the Mecoptera, with the rank of a Suborder. No 

 Mecopteron is yet known with a basal branch of Sc present, 

 as in Aristopsyehe; so that, in this character, the Archetype of 

 the Paratrichoptera is more archaic than that of the Mecoptera. 

 The cubito-median Y-vein is not clearly preserved in any of the 

 four known genera, but appears to have been lost by fusion of 

 Cuj with Mj_ 4 in Aristopsyehe, as far as this part of the wing 

 can lie made out. However, we have already seen how this 

 structure turns up in the more archaic forms of other Orders 

 of the Complex (Section iii.) . Hence I have included it in the 

 Archetypic characters, with the firm belief that further fossil 

 finds in this Order will show that it was present. 



The Paratrichoptera are specialised from the original Meeop- 

 terous type by their distinctly Trichopterous fades, which is 

 most marked in the shortening of the apical forks belonging to 

 Ks and M 1 _ 4) and the consequent formation of the radial and 

 median cells ( re, me), and the veins arising from them, on 

 strictly Trichopterous lines. As regards the median cell, it 

 should be borne in mind that the Diptera also share this charac- 

 ter with the Trichoptera ; and there can be no doubt that this 

 was also the case with the radial cell in the Diptera, before 

 specialisation set in and removed one of the four branches of 

 Rs. As regards the cubitus, the Paratrichoptera differ strongly 

 from the Trichoptera, but agree with the Mecoptera and Diptera, 

 in having Cu 1 running straight to the wing-border, without any 



