74 
Psyche 
[September 
but its position is very different. In the Archizygoptera the nodus is 
very remote from the pterostigma and close to the base of the wing, 
the subcosta being very short. In T riassothemis , the nodus is close to 
the pterostigma and probably at about the middle of the complete 
wing. The nodal area is so clearly preserved in the specimen of Tri- 
assothemis that there can be no doubt about its structure; although 
the subcosta has been broken away just before its termination, it is 
present on each side of this missing section. The distal location of 
the nodus apparently eliminates T riassothemis from the Archizygop- 
tera, as the suborder is presently understood. Another peculiarity of 
the wing of T riassothemis is the widening of the area between Ri 
and the costal margin of the wing, just beyond the nodus. That this 
is not a distortion is shown by the normal location and distribution 
of the cross-veins and the other veins in the anterior part of the wing. 
The pterostigma is like that of the Archizygoptera and the several 
branches of the radial sector have the divergent arrangements char- 
acteristic of that suborder, although the divergences are not quite so 
marked. The absence of a distinct anal vein (at least in the part of 
the wing which is preserved) is also suggestive of the Archizygoptera. 
In most respects, therefore, Triass ot he mis possesses many of the char- 
acteristics which we find in the wings of the Archizygoptera but the 
location of the nodus is very different from that of all of the genera 
of this suborder so far known. 
The small apical fragment of a wing, which is located on the same 
piece of the rock as T riassothemis, resembles the latter in so far as 
the known parts of the venation are concerned (Figure ib). Ri, 
R2, IR2 are arranged about as in mendozensis but there is a clear 
indication that the next vein, R3, would be somewhat more remote 
from IR2 than it is in the specimen of mendozensis. The pterostigma 
is like that of mendozensis so far as its distal part is concerned, but it 
appears to extend proximally the full length of the preserved part of 
the wing, as shown in figure ib. It seems very likely that this small 
wing fragment represents an odonate closely related to T riassothemis 
mendozensis ; in fact, since we do not know anything about the dif- 
ferences between the fore and hind wings of the Archizygoptera, it 
is possible that the fragment is part of another wing of the type of 
mendozensis. 
The discovery of this piece of Triassic rock containing two fossil 
insects, even though they are in fragmentary condition, points up the 
possible significance of Triassic strata in the Mendoza region of 
Argentina as a source of extensive collections of insects. Wieland 
