BY R. J. TILLYARD. 635 



Order PROTOMECOPTERA. (Plate Ixvii., fig,s.9-]0). 



We have already described above the condition of the trichi- 

 atioii in the wing of the Triassic fossil ArrhipaH.orpa, the only 

 known representative of this Ordej". 



It will be seen that 

 this wing differs from all .'.* -'•* ;•' ;-' *:•.''•' 



known Holometabola at ''. . : - ; .':..;,.* .-*■.* .'•; ■'. 



present existing in hav V'" •. v- ' l',;* •_';. •'■' 

 ing the archedictyon ; '...•' V. '.\- \' ■;'■':'. ■'/. 



still present, upon all •,• •'. ;.;'•. •;.' ••.■••.."'.• '.'■!■ 



parts of the wing-mem- •/:. •'.■ .. ..-. .v.-'; "'' .•/•/. 

 l)rane, in an aphanto- .' v;. '.•:v.*';-. '-': ':'/'' \: 

 neuric condition, and .*.'. V'v '. • J; ;, ■•; •'•., 

 carrying macrotrichia ' •',•; • '■'.' .'•:- ':;-.'r'^r-' -'/'.' 

 upon it, mostly at the *;; vv '•/.'' \:' •'.'■ •••*. 



junctions of two or more ;•' V-. ■;*":'..■ .' .•'. ;; -^ 



venules. '":^ '.'''•'' V .." ••: ■:'.. '.V 



Further, it should be '," '.• •.' •'}' /.' "'■',' 



noted that both macro- V! .'.•."'■- '*•"■.• ::•'.*' '•■■ 



trichia and microti'ichia 



are considerably largei- Text-fig. 21.* 



in this fossil than in other Holometabola. The tendency towards 

 reduction in size can be seen to be operating independently in all 

 Orders; it culminates, in the case of tlie microtrichia, in their 

 complete elimination from the wings of the higher families of the 

 Planipennia and Lepidoptera; and, in the case of the macrotri- 

 chia, in a great reduction in their number and shortening in tlieir 

 length, in the case of the Diptera and certain Mecoptera. 



Order MEGALOPTERA. (Text-fig. 22), 



The most archaic members of this family exhibit a near ap- 

 proach, in arrangement of the trichiation, to that seen in the 

 Protomecoptera, We have selected the genus Archichau/lodes as 



* Arrangement of the bases of insertion of the scales on a small portion 

 of the wing of the Hawk- Moth C'crqaosa triangidaris Don., to show the 

 pattern of the lost archedictyon; { x 50). 



