BY R. J. TILLYARD. 721 



to argue that the present-day broad hindwing and specialised anal 

 loop of the Libellulince was developed secondarily from a wing in 

 which the original broad Anisopterous hindwing had been reduced 

 to approximately equal width with the forewing. If not, we should 

 rather accept a theory of the development of all the present-day 

 loops from a broad-winged but very generalised archaic type, to 

 which Chlorogomphus may hold the clue, and regard all the nar- 

 row-winged forms, even if proved archaic, to be the result of asthe- 

 nogenetic convergence. The former theory is strongly held by Dr. 

 Ris, whose opinion, as without doubt that of the most accomplished 

 Odonatologist of the present day, cannot be lightly put aside. To 

 me, however, the latter seems to be by far the more probable. 



Let us first of all, therefore, compare both larval and imaginal 

 forms of Nannopldehia and Cordulephya* : — 



A. Larvae: — 



(1) The labia. — These are very distinct, Cordulephya showing 

 high specialisation in several points. Com^Dare a, the long narrow 

 gulf-like incisions of the upper part of the inner margin of the 

 lateral lobe in Cordulephya, with the normal crenations of Nanno- 

 phlebia; b, the much longer end-hook in Cordulephya; c, the more 

 numerous and more strongly developed setae, both lateral and men- 

 tal, in Cordulephya; d, the larger number of spines (3-4), on the 

 lower (normal) crenations of Cordulephya; e, the finely speckled 

 or spotted surface of the lateral lobes in Cordulephya, with the few 

 but larger and more conspicuous black spots on Nannophlebia. 

 One cannot but conclude that Nannophlebia is really more closely 

 allied, in its labium, to the main Eucordulian stock, than it is to the 

 distinctly aberrant Cordulephya. 



(2) The antennce. — Though both are seven-jointed, those of 

 Nannophlebia are very much shorter than those of Cordelphya. 



(3) The legs. — Those of Cordulephya are very much the longer. 



(4) The abdomen. — In Cordulephya, segment 10 is fully recessed 

 into 9; while in Nannophlebia, it is normal in position. [The ar- 



* For characters of Cordvhphya, see Plates xi. and xii., pp. 421-2, These 

 Proceedings, Vol. xxxvi., Part 2, 1911. 



