IV] THE LARVA OR NYMPH 85 



regular crenations, each crest armed with a set of small setae ; and 

 (c) iheLibelluline (fig. 32 N) in which the crenations are smoothed 

 out and the distal border becomes more or less straight, with setae 

 marking the original notches. Three peculiar aberrations from 

 the main developmental line are figured in fig. 32 M, P, Q. Epoph- 

 thalmia and Azuma (M) are highly specialized Macromian types, 

 in which the distal border has become hypertrophied, forming 

 a set of huge teeth which do not interlock with their fellows on 

 the opposite' side. This is a most formidable and peculiar weapon. 

 Austrocordulia (p) is the only known Idocordulian labium, but is 

 probably not typical. Four or five large irregular rounded lobes, 

 carrying sets of setae, lie along the distal border. Cordulephya (Q) 

 is a highly specialized Eucordulian type, in which deep narrow 

 indentations are formed along the upper half of the distal border. 

 These do not interlock, but form a kind of sieve for the ejection of 

 pieces during mastication. Warts (fig. 32 N) occur on many masks 

 of type (ix). A reference to fig. 29, E and F, will shew how the 

 concave mask excels the flat form in hiding the whole face. It 

 must, however, be added that the Aeschnine labium is far more 

 effective for the capture of large prey, both as to reach and as to 

 the efficacy of its hooks. The concave labium seems more adapted 

 for catching very small animals. 



The Thorax (fig. 29A-o). 



The short but well-formed prothorax of the larva is always 

 larger than in the imago. It is often armoured with projecting 

 tubercles or spines. In the Aeschninae two such spines, placed 

 close together above the procoxa, form the supracoxal armature, 

 a structure of considerable systematic importance, especially in 

 the genus Aeschna (p. 350 and fig. 180). The plates of the neck 

 or microthorax are well-developed. 



The synthorax is strongly formed, with the parts closely fused 

 in the well-grown larva. The secondary divisions of the pleurae 

 are only weakly indicated. The mesostigmata (sp-^ are placed 

 latero-dorsally between prothorax and mesothorax, on two 

 flattened pieces called the mesostigmatic laminae; these fuse 

 together in the imago to form the spiracular dorsum. The pleural 



