446 NEW AND RARE AUSTRALIAN AGRIONID^, 



position of equilibrium with the highest development of the 

 group. In the asthenogenetic offshoots, we find it again shifted 

 back away from the arculus towards the base. 



/'. The form of the pterostujma. — Regularity of pterostigma char- 

 acterises the older forms. As the group reaches its highest point 

 of development, convex, trapezoidal, and even abnormal forms 

 occur, and, in the genera Isclinura and Ayriocnemis, we find a 

 differentiation in the colouration of the pterosti<(ma in fore and 

 hiudwiugs. 



Apart from venation-characters, let us now consider: — 

 ii. Constant hispxual characters. — The most important are : — 

 a. General build or facies. —deduction in size of head, strength 

 of thorax, size of legs, loss of inferior tooth on the tarsal claw, 

 and extreme attenuation of abdomen, are all parts of the general 

 asthenogenetic process. The four main divisions, suggested by a 

 and h of the venational characters, will l)e found to coincide 

 almost exactly with divisions made on character of facies. Argia 

 and allies are the most robust insects, possessing also the longest 

 le^s; next to these, come A(/rion and Ischmira; then the insects 

 of distinctly slenderer build comprised in Pseudayrion and allies; 

 and fiiuilly the extremely slender Telehasis group (excluding ^(/?'t- 

 ocnemis) with the inferior tootli of the tarsal claw absent, 



h. Correlated secondary sexual characters. — 1\\ this legion, the 

 primitive forcipate form of the appendages of the male has long 

 been lost, aiid we find an immense variety in the form of these 

 organs. They are usually very short and irregular in form, and 

 would be absolutely useless as claspers to hold the female, were it 

 not that there is a correlated development of the female pro- 

 thorax, whose sculpture is so arranged that the appendages of 

 the male fit closely into it and are held tightly by it. Deep holes 

 and pits, elevated tubercles, horns and hooks on the prothorax 

 all play tlieir part in this group as correlations of {-articular forms 

 of appendages in the males. It is, therefore, an incorrect use of 

 characters to employ one of these without the other for generic 

 purposes, as de 8elys has done, for instance, in Pseudayrion. and 

 allies. The two must be used together. 



