BY R. J. TILLYARD. 225 



In the hinchvhig, the dilatation of the base of the costa is quite evident, though 

 smaller than in the fore^\ing. Se is forked distally. There are three or more 

 "apparent" sectors of R, very irregular in form and position. M is not fused 

 with R basally, hut can he seen as a very weak concave vein running below it. 

 Mr, is strongly formed, arising from M at an agle of about 60° with M1-4. C'ui 

 is unbrauohed, diverging distally from Cu2 so as to carry a double row of cells 

 between them for the distal third of their lengths. Cu2 lies in the cubito-anal 

 furrow, except for a very short apical portion. lA arises separately from Cu 

 but very close under it; it gradually approaches Cu, and then fuses with it in 

 the anal furrow for a considerable distance near the middle of the wing, finally 

 diverging from it again. 2A is forked not far from the base, and 3A has 

 numerous Ijriinches on the anal fan. The cubito-anal furrow divides the wing 

 into approximately two e(|ual halves longitudinally; the contour of the distal 

 half of the wing, from the apex of Sc to the posterior angle of the anal fan, 

 is very nearly semi-circular. 



Genotype, Thaumatoperla robiosta^ n.sp., from Warburton, Victoria. 



Apart from certain very evident specialisations in the wing-venation, this 

 remarkable genus is perhaps the most archaic type of Stonefly at present exist- 

 ing, and might in many respects be regarded as a true Protorthopteron. It 

 seems quite likely that a careful study of some of the large Protorthojitera of 

 the Upper Carboniferous, especially those from Mazon Creek, may reveal a close 

 affinity with this genus. Characters evidently of great anticiuity in the venation 

 are the very strong development of M5 and the strong formation of the cubito- 

 median Y-vein : also the jirimitive condition of Cu2, which has not yet fully 

 aligned itself into the cubito-anal groove of the wing. The well marked but 

 irregiilar cro.ss-venation, which is equally in evidence over all parts of both 

 wings, appears to be a true archedictyon of Palaeodictyopterous or Protorthop- 

 terous origin and a feature of great antiquity. The genus is also far more 

 archaic than any other known Stonefly in having about one-half of the area 

 of the hindwing occupied by the veins above the cubito-anal furrow. There is 

 also the same marked tendency towards variation in the details of venation 

 which is found in other archaic insects, such as the Cockroaches; and this varia- 

 tion is particularly noticeable in comparing the two sides of the same insect. 



A high specialisation of the venation is to be seen in the remarkable for- 

 mation of the branches of the radius, which compares closely with that seen, 

 in the forewings only, in the family Hemerobiidae of the Order Planipennia. 

 It would appear that the true radial sector has become completely fused with the 

 main stem of R, so that its branches come off as separate sectors. In such a 

 case, it is usual to call these branches "apparent" radial sectors, and to state 

 their numl)er. Other specialisations are the great amount of fusion of R and 

 M basally in the forewing, the fusion of Cu with lA basally in the same wing, and 

 a curious formation to be seen in the left hindwing only, in which the most 

 basal of the "apparent" radial sectors has quite lost its connection with R, and 

 is attached to M. In the right hindwing, a strong oblique cross-vein indicates the 

 manner in which this vein-capture has been brought about. 



The characters of this genus are perhaps so distinct as to justify tlic for- 

 mation of a separate family for its reception. I have, however, determined to 

 keep it for the present within the Eu.^theiiiirlae, as the genus Exxthruiopsis, 

 n.g., is its nearest ally, and the only genus with which it shows anv real 

 afBnitv. 



