BY R. J. TILLYAKD. 243 



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about three-fifths of the length of the wing, as against one-half 

 in Belmontia. This difference could easily be removed in the 

 course of evolution, either by actual growth of Sc, or by a re- 

 duction in the length of the apical portion of the wing. 



In spite of the extra veins present in the radial area of 

 Belmontia, the resemblance of this part of the wing to that of 

 Rhyacophila is very striking. In both, R x is connected with 

 Sc 2 above, and with R 2 below, by cross-veins in closely similar 

 positions. The form and manner of origin of R2+3 is practically 

 the same in both; but Belmontia possesses an extra vein, R 3b , 

 which has been completely eliminated from Rhyacophila and all 

 other Trichoptera. The common stalk R4+5 is exceptionally 

 short in Belmontia. But the tendency of such stalks throughout 

 the whole of the Orders Trichoptera and Lepidoptera is to 

 lengthen; so that the condition found in Rhyacophila is a natural 

 derivative from this, as part of the same process by which the 

 extra branches of R 5 have also been eliminated. Cross- veins are 

 absent from this part of the wing in Rhyacophila; but there are 

 many other existing genera of Trichoptera in which the inter- 

 radial cross-vein (ir) is present, closing the radial or discoidal 

 cell distally. 



In Belmontia there are four cross-veins between R, or Rs, and 

 M. One of these lies just above the origin of the arculus, and 

 is absent from Rhyacophila. The other three connect Rs or its 

 most posterior branches with M 1+ 2 or M a . Only the middle of 

 these three {r-m) remains in Rhyacophila. 



The media itself is very similar in Belmontia and in Rhya- 

 cophila, the only difference being the extra distal forking of 

 M 4 in Belmontia. The position of the median fork (mf), not far 

 from the middle of the w-ing, and the relative positions of the 

 distal forkings, are much the same in both. In Belmontia, as in 

 numerous existing genera of Trichoptera, though not in Rhya- 

 cophila, the median cell (mc) is closed by the inter-median cross- 

 vein (im); there is also a cross-vein within this cell itself, and 

 cross- veins connecting M 3 with M 2 , and M 3 with M 4 , respectively, 

 which are absent from all recent Trichoptera. 



Of the cross- veins connecting M 4 with Cu, m-cu is present in 



