244 FOSSIL INSECT WING, ORDEK PA KAMEOOPTEKA, 



Rhyacophila, but has moved slightly basad, to take up a more 

 advantageous position at the actual forking of M34-4 into M a and 

 M 4 . The more distal cross-vein, with its continuation across 

 Cu la to Cu lb , is missing in Rhyacophila, as in all existing Tri- 

 choptera. 



The general scheme of the cubitus is the same in Behnontia 

 and in Rhyacophila. The cubital fork (cuf) lies at a level 

 slightly basad from the origin of pa, and the bent portion of 

 Cu, arising from the fork is similar in both. The course of the 

 strong, straight, convex vein Cu, beyond its junction with pa is 

 the same in both; but the apical fork of this vein is larger in 

 Rhyacophila than in Bclmontia. It is quite clear that a slight 

 movement of the median fork distad, with reduction of the fourth 

 apical fork (between M ; , and M 4 ), correlated with a slight move- 

 ment of the secondary cubital fork {cuf) basad, and consequent 

 change in the position of m-cu, would account for the changes in 

 this region, and could easily have taken place during the period 

 of time elapsing between the Upper Permian and the first ap- 

 pearance of Rhyacophila and its allies. 



The intercubital cross-vein (icu) is absent from Rhyacophila, 

 but present in Behnontia; the cubito-anal cross-vein (cu-a) is 

 present in both, but has moved much further basad in Rhya- 

 cophila. 



Finally, in Rhyacophila, as in all existing Trichoptera, the anal 

 area of the forewing has undergone very high specialisation, the 

 three anal veins having become linked up with one another by 

 loss of the distal ends of 2A and 3A, and incorporation of the 

 cross-veins ia x , ia 2 in the complex trifurcate vein that is found 

 universally in this region of the forewing of all true Trichoptera. 

 The condition of the anal area in Belmontia is the typical 

 archaic condition, from which it has long been clearly evident 

 that such a type of specialisation must have been originally 

 derived. 



Unfortunately the area of the jugal lobe, if such exists, is 

 covered over in the fossil; so that we cannot say definitely 

 whether it was triangular, as in Rhyacophila, or rounded and 

 less prominent, as in Chorista and allies. 



