BY R. J. TILLYARD. 633 



distal Y-vein (Section vi.). This character is best shown in the 

 Hepialidae. 



(8) The cubitus is three-branched, Cuj forking distally as in 

 the Paramecoptera, Megaloptera, and Trichoptera. 



(9) In the hindwing, 1A fuses with Cu 2 not far from its origin 

 for a short distance, and then diverges from it again. This 

 character is to be seen in the Jugo-frenata, Hepialidae and in 

 quite a number of the older Heteroneura. It also occurs in all 

 Mecoptera and Trichoptera, in the Raphidioidea and some Plani- 

 pennia. 



(10) In the forewing, 2A is looped on to 1A, and 3A on to 2A, 

 thus forming a double Y-vein as in Trichoptera. This character 

 is to be found in Mnemonica and Sabatinea, the two most archaic 

 genera in the Jugo-frenata, but is usually reduced to a single 

 Y-vein, formed by 1A and 2A only, in the other genera of that 

 group. Throughout the Lepidoptera, 3A tends to become ob- 

 solete in the forewing, and is absent from most forms, including 

 the Hepialidae. 



( 11 ) There is only one costal veinlet, viz. the humeral, hm. 

 In many pupal wings, this is seen to be supplied by a special 

 trachea running alongside Sc. (Text-figs. 80, 85) . This is cer- 

 tainly the homologue of the formation to be seen in the Para- 

 trichoptera (Test-fig. 65) . 



(12) The cross-vein system is even more reduced than in the 

 Archetype of the Trichoptera, only the following being present: 

 — the subcosto-radial (sc-r) ; the inter-radial (?V) closing the 

 radial cell (re) distally; the radio-median (r-m) ; the inter-median 

 (im) closing the median cell (me) distally; the cubito-anal 

 (cu-a) ; the first inter-anal (ia-y); the second inter-anal (iav) 

 in the hindwing, and the sub-anal (sa) in the forewing only. 

 This last is only to be seen in Eriocrania (27, and Text-fig. 53, c). 



Thus, quite apart from the six unnamed cross-veins which, 

 since they are present in the Rhyacophilid genus Psilochorema 

 have also been included in the venation of the Archetype of the 

 Trichoptera, the following cross-veins present in that Archetype 

 are absent from the Archetype of the Lepidoptera: — the sub- 

 humeral (sh) ; the inter-radial from 'R l to R 2 (?>') ; the medio- 

 cubital (m-cu). — owing, of course, to the fusion of M 4 with Cu la ; 

 and the inter-cubital (ieu) . Thus the cross-vein system of the 

 Lepidoptera is archetypically considerably more reduced than 

 that of the Trichoptera. 



