188 DEVELOPMENT OF THE WING-VENATION OF ODONATA, 



to catch the systematist who pins his faith to imaginal wing- 

 venation only. That such may be reasonably expected to occur, 

 will be seen by perusing Section l> of this part, in which a most 

 unexpected and extraordinarily well hidden convergence is 

 brought to light in the Agrionidcf. 



To return to Austrogomphus^ it is now necessary to propose a 

 subdivision of this genus into two, as follows : — 



(1.) Distal side of anal triangle in the male descending per- 

 pendicularly from Ac (Fig. 17). Larva with flattened abdomen, 

 four-jointed antennae only moderately swollen, and rectal tracheal 

 gills without papillae. Larva lives in trash in running streams. 

 Genus Austrogomphus. 



Type, Austrogomphus guerini Ramb. 



This genus includes, most probably, all the species at present 

 grouped under the name Austrogomphus, except the three 

 separated out below. 



(2.) Distal side of anal triangle in the male descending from A' 

 before the level of Ac, and running in a slanting curve away 

 from it(Fig.l8). [.arva with rounded abdomen, four-jointed 

 antennje (in which the third joint is greatly swollen and rounded, 

 while the fourth joint is practically obsolete), and rectal tracheal 

 gills with numerous papillte. Larva lives completely buried in 

 clean sand in running streams. 



Genus Hemigomphus Selys (re-defined*). 



Type, Austrogomphus heteroclitus Selys. 



This genus, w^hich corresponds to the second division of de 

 Selys' suppressed genus IIemigom,phus, includes only three species, 

 viz., A. heteroclit'tis Selys, A. comitatus Tillyard, and A. armiger 

 Tillyard. 



Hemigomphus is, almost certainly, an offshoot from the Palae- 

 arctic Onychogomphus-growp, with which it agrees in the form 

 of its larval antennae and rectal gills. It has, however, suffered 



* The generic iiaine Heniigomphtts was intro<Uiced by de 8elys (type H. 

 heteroclitus), but suppressed bj' R. Martin owing to the ver\' slight diflFer- 

 ences between it and Austroyomphus. The new definition of the genus 

 iiere given, however, establishes it on a firm footing. 



