38 
Psyche 
[March 
The prothorax possessed a pair of lobes, which were usually cordate, 
and which were narrowly attached to the pronotum along a cuticular 
ridge. In most cases the lobes appear to have been membranous and 
to have possessed longitudinal as well as cross veins; the veins arose 
from the basal cuticular ridge and radiated into the lobe, some of 
them branching. In the fossils the convexities and concavities of 
the veins are not visible, and they were presumably not present in 
the original specimens. In exceptional instances^ the lobes may be 
heavily sclerotized, all traces of the veins being lost. The lobes 
usually overlap the basal parts of the fore wings to a considerable 
extent; being situated high on the prothorax, they may have acted 
as immovable “fore sails”, air passing under them and increasing 
the pressure on the functional wings. Prothoracic lobes of the Palaeo- 
dictyoptera were undoubtedly homologous with the functional wings; 
there is no evidence that they were used for active flight, the basal 
articulation and the distribution of the veins being unlike those of 
the functional wings. 
The legs of the Palaeodictyoptera were relatively short or even 
very short and usually stout. The tibiae were slightly elongate,, 
often spiny, and the tarsus was composed of five, subequal segments; 
two claws and an arolium were present in at least some species. The 
tibiae in some specimens show what appears to be a separate segment 
proximally, set off by a suture from the rest of the tibia; this seems 
to be comparable to the structure of the tibia in many existing 
Ephemeroptera. The three pairs of legs are similar except that the 
hind pair are slightly longer. The legs so far as known were adapted 
for walking and presumably were also used for holding onto 
vegetation or for climbing. 
The wings of the Palaeodictyoptera had great diversity in size 
and shape. There are some species in which both pairs of wings 
were almost equal, others in which the hind wings were somewhat 
enlarged and then still others in which the hind wings were greatly 
enlarged. In several isolated lines of families, there was a tendency 
for the hind wings to be reduced, with respect to both width and 
length or a combination of both. The shape of the wing also extends 
over a very wide range, from relatively short to very long and 
slender. The articulation of the wings with the thorax is not pre- 
served in detail in any specimens but it seems to be comparable to 
that in the existing Palaeoptera, the Ephemeroptera and Odonata. 
The convexity and concavity of the longitudinal veins is well known 
in the Palaeodictyoptera; a postcostal or a precostal area is present 
