228 WING-VENATION IN ZYGOPTEROUS DRAGONFLIES, 



cuticularisation gradually overspi-ead the base of the trachea, it 

 continued to grow out under the main stem of M, and finally 

 became united with a strong, slanting cross-vein from R, below 

 the subnodus, thus forming a veritable radial sector on the wing- 

 case itself, though the trachea Ms remained attached to M. 

 Three stages in this growth are shown in Fig.5. These were 



^ drawn from the two Wentworth 



^*^ ■_ ' " "^^^^^ ^^^^■•■ns"' Falls larvte in the last instar. It 



'^^^^^^^^^^^^^^^^^^ cII'' is important to note that the con- 



7**^ -Cu, nection with R was effected on 



^"'^ the underside of the wing-case, 



Text-fig. 6.* • ^1 • j^ ^ 1 



snice this seems to show an ob- 

 vious difference of level between tracheie R and M in the larval 

 wing, and helps us to understand how, in Anisoptera, Rs was 

 able to pass below Mj.o without becoming strangled by the pres- 

 sure of these overlying tracheae. 



In conclusion, I offer an amended dichotomous table for the 

 classification of the Zygoptera, based on venational characters, 

 with particular reference to the points mentioned in this paper: — 



[R once-branched. M with three posterior branches. Discoidal cell 



divided into triangle f-supertriangle Suborder Anisoptera. 



■ , R unbranched. M with four posterior branches. Discoidal cell a 



I simple quadrilateral Suborder Zygoptera (2). 



J Ms arising from M.,; a long bridge developed backwards from this 



2, J point Family Lkstid^e (3). 



I Ms arising from the main stem of M. No long bridge 4. 



r The long bridge runs back to meet Mjo - 5- 



'\The long bridge runs back to meet Mg 6. 



'Mg and Ms close to arculus; Mj at subnodus. More than two ante- 



nodals Family CAL0PTKRYGiD^t(7). 



Mj and Ms close to subnodus (one of them usually directly under it), 

 M.^ distally placed from subnodus. Normally two antenodals, 

 rarely more {Tliatimatoneura, fossils, and occasional anomalies)... 



Family Agrionid^(8). 



* Diphlehia lestohies Selys. Last larval instar. To show method of 

 cuticularisation of A' backwards from Ac towards base of wing. (Camera- 

 lucida drawing.) Compare PI. xxxiii., fig. 3. 



t Fossil forms of this family are omitted. 



