BY R. J. IILLYARD. 



587 



forming the upper arm of the distal Y-vein is only a cross-vein* 

 Bui a little consideration will show that the case is exactly 

 on a level with that of the eubito-median Y-vein, in which M5 

 was originally considered to be only a cross-vein, until the dis- 

 covery of the fossil Belmontia proved it to be a main vein. In 

 the fossil Archipanorpa (Text-fig. 57), the vein M 4 descends at 

 right angles from the median cell, and would naturally be taken 

 for a cross-vein, were it not for its very strong formation, and 



Text-Fig. 57. 

 Portion of the hindwing of the fossil Archipanorpa (Order Protome- 

 coptera) to show the partial fusion of M4 with Cui a , and the trans- 

 verse position of the former vein. The small circles indicate the 

 positions of the macrotrichial sockets. Note their absence from the 

 true cross-vein x. Lettering as on p. 535. (x 10.) 



the very evident sockets of the macrotrichia which are still pre- 

 served upon it. Thus M 4 in this fossil shows an even more 

 advanced condition than that seen in the Hepialidae, as regards 

 its direction; and yet there can be no doubt that it is a main 

 vein . 



Having examined the pupal wings of a number of Hepialidae, 

 at various stages of development, and still failing to find any 

 signs of trachea M 4 , it occurred to me that it might very pro- 

 bably develop at metamorphosis, in the same manner as trachea 

 M s . For this purpose, I obtained a large number of freshly 

 emerged imagines of Hepialidae, from which I prepared cleared 

 mounts of the wings. The result showed that, although, in the 

 majority of eases, trachea M 4 is not present, yet there were a 

 considerable number of specimens in which it w y as present. In 



*See the Note on this point on p. 652. 



