96 CAUDAL GILLS OF ZYGOPTERID LARVAE, 



Nodal spines only moderately large, those of inner border almost 

 as large; nodal line oblique, especialh' so from mid-rib to inner 

 edge. Colour of gills dull brownish or yellowish, crossed with 

 two bands of brown oi' grey pigment, one at node, and the other 

 half-way between node and tip (Plate ii., fig. 14). 



The gills of the Pala^arctic Erythromma najas Hansemann, 

 appear to resemble most closely those of Caliagriou. Under the 

 present classification, Er)/fhromma ia\h into the Tribe Ai/rio7uni, 

 on account of its wing-venation, whereas the three Australian 

 genera belong to the Tribe Psendagrion'uii. It is interesting, 

 therefore, to note that, in its wing-venation, Caliac/rion ap- 

 proaches most closely of the three to the venational stage which 

 separates the Aiirionini from the PfiPiidagnouini. 



y. The Suhnodafp VfirficaJ La me/ /a 

 (Text-fig.25: Plate ii., Iigs.l5, !()). 



A stage further on in the process of the elimination of the 

 suture of the originally two-Jointed lamella may be seen in the 

 sulmodatr form of gill, which occurs in the genera Isehnnra and 



Text-fig. 25. 



Subnodate gills of I><chmira Jieterosficta Buvm. . in natural position, 



lateral view; ( x 6). 



Ceriagrion. Here the original nodal constriction is lost, but the 

 position of the node is still clearly marked by the sharp ending 

 of the row of spines along the outer edge of the gill. Con- 

 currently with this, the gill becomes definitely pointed, with the 

 branch tracheae coming oft' from the main stems very obliquely? 

 and more regularly than in the nodate form of gill; while the 

 dendritic form of the end-branches, though still present, is not 

 by any means so noticeable. Small spines are present on the 



