194 MKSOZOIC IxVSECTS OF (QUEENSLAND, l., 



(2) Polygonal tneshivork of the iviny-membraiLe — Turning from 

 the vein to the membrane alongside it, we notice at once that 

 this is not smootli, but is thrown into innumerable pits and 

 ridges, with tuljercles appearing upon the latter in many places. 

 Tn places where this structure is well-preserved, it will be seen 

 that the ridges form an irregular polygonal tneshivork, enclosing 

 sunken areas or cellules (shaded in Plate A-iii., fig. 6). The large 

 tubercles, which resemble those of the veins, are seated princi- 

 pally upon the swollen junctions of the ridges. The ridges are 

 not as well-defined as actual veinlets would be, except here and 

 there (Text-tig.66, cv), where a particularly strong and straight 

 ridge may be seen running out for some distance from a main 

 vein. Nor are their tubercles usually as well-defined as are 

 those of the main veins. 

 ^ ^ ^ The area show ;i diagrammatical ly in Plate 



"'---( j,y*v/'--;'' viii., fig. 6, was selected from near one of the 

 main veins on the basal portion of the pre- 

 served part of the wing. It is a typical 

 /'S '; /'V""!"\"Y' unspecialised mesh work. But, in most parts 



I " of the wing, and especially towards the distal 



■,.'\ ,-\ \^\J\\ end, the polygons of the mesh work tend to 

 '''\ ,'- '\ \ \ \ become stretched out transversely and some- 

 \ A\ 1 'A \ \r what obliquely to the main veins. This is 

 . y-Vl.^ /""%. V-( ' represented diagrammatically in Text-fig.66, 

 \ \X\'l^.^,-\ \ Y * whereas Text-fig. 6ft corresponds with the un- 

 specialised portion shown in Plate viii., fig. 6. 





-*•. The only conclusion that I can come to, 



Text fii' H-* fi'om a study of these peculiar structures, is 



that the ridges represent the original Palceo- 



dictyopterous meshwork of veinlets iti a degenerating stage. The 



* Diagrams of the Palseodictyopterous meshwork upon the membrane of 

 the wing of Arcliipaiiorpa magniffca, n.g. et sp., — a, from near base of 

 preserved portion of wing (corresponding with Plate viii., fig. 6); h, fi-om 

 distal portion of wing, showing tendencj'' of the mesh to hecome stretched 

 transversely and somewhat obliquelj'^ across the wing, ( x 20); cr, a strong 

 cross-vein, not yet ohliterated; nir, main vein, with macrotrichia omitted. 

 The figure is intended to show only the pOf<itioH; and not the structure of 

 the meshwork. 



