BY R. J. TILL YARD. 407 



GifOUP ii. Idocokdulina. Larva smootli; with smaller head 

 and thorax, short legs, very flat labium; labium with deei) 

 irregular incisions, no warts or dots, and few mental or lateral 

 setae. 



Imaijo usually of weak flight, with smaller head and thorax, 

 short legs, usually slender cylindrical abdomen; wing-venation 

 with smaller free triangles and subtriangle, incomplete recession 

 of hindwing-triaiii^le, fairlv short or (juite short anal looj), shew- 

 ing no longitudinal bisector. 



Group iii. Macromina. Larva smooth, with nearly circular 

 and very flattened abrlomen, very long legs, head with a pyrami- 

 dal frontal horn; labium with deep dentition of lateral lobes. 



Imago: large insects of strong flight, and robust development; 

 wing-venation with small triangles far removed fiom arculus, 

 basilar space free, anal loop broad and compact. 



Group iv. Hvntiiemina. I^arva very villose, with elongate- 

 oval body, short legs, and divergent wing-cases, head scjuare in 

 front, with projecting eyes. Imago: insects of weak flight, and 

 slender-build; wing-venation with dense or fairly dense reticula- 

 tion, basilar space reticulated, hind wing-triangle usually not 

 retracted to level of arculus, anal loop very broad and slioi't, 

 never as long as wide. 



The genus Vorduhphyn is obviously not at all closely 

 related to either the Marrfnuum or Sgiitlu mnia. We should, 

 therefore, consider whether it is closely enough allied to either 

 the Eucorduliiia or hlocorduIiiKt to warrant its inclusion in 

 one of them ; or whether, perhaps, it shews a sufficiently 

 independent development to deserve coordinate rank by itself. 

 This is a very difficult problem, as it will be seen that the 

 evidence is in many respects contradictoi'y. It is, however, a 

 problem of deep interest, and brings out some very interest- 

 ing points in Odonate evolution. I propose to consider the 

 evidence in detail aff'orded by the consideration of (i.) the 

 early stages, (ii.) the form of tlie imago, (iii.) the wing-venation, 

 (iv.) a comparison of the two known species of the genus. 



