BY K. J. TILLYARD. 



629 



other five are more doubtful, and are only provisionally in- 

 cluded until more is known about the venation of these very 

 ancient Rhyacophilids . 



(2) The cross-vein sa occurs, so far as I am aware, only in 

 the genus Philopotamus. But, as a cross-vein occurs in a closely 

 similar position in the archaic Lepidopterous genus Eriocrania, 

 1 have decided to include it, under the name of subanal cross- 

 vein, in the Archetypes of both Orders. 



(3) In spite of the formation of the anal Y-vein between 1 A 

 and 2A in the forewing, the first inter-anal (iai) may still be 

 seen clearly present in a number of genera, as also in Sabatinca 

 and Trictena amongst the Homoneurous Lepidoptera. There is 

 therefore no doubt that this cross-vein is an archetypie charac- 

 ter. 



Having, then, determined the Archetype of the Order, we may 

 now briefly indicate the main lines of specialisation in the wing- 

 venation within the Order itself. These may be stated as fol- 

 lows : — 



(1) Broadening of the anal area of the hindwing. In the 

 most archaic family, the Rhyacophilidae, fore and hindwings 

 are closely similar in shape, and the anal area of the hindwing 

 only differs from that of the fore in having 1A fused near its 

 base with Cu 2 , and the courses of the three anal veins running 

 separate and free to the wing-border, with the two inter-anal 



Text-Fig.73. 

 Hindwing of an undescribed species belonging to the family Polycentro- 

 pidae, allied to Stenopsychod.es Ulm. , showing the enlarged anal 

 area. Lettering as on p. 535. (x 8). 



