1970] 
Kukalova — Palaeodictyoptera 
37 
veins. Archedictyon sparse, more like irregular cross veins con- 
nected with anastomoses. 
Microdictya villeneuvei differs from all other species in the pro- 
nounced curvature of the distal part of the posterior margin. 
Summary 
The Commentry shales in central France provide us with the 
most extensive and the best preserved collection of Palaeodictyoptera 
so far known. The information obtained from detailed study of 
these fossils shows that this extinct order was a very diverse one, 
with far more specialization and adaptations than have previously 
been suspected. The following is a general account of the structure 
of the Palaeodictyoptera, as it is now known. 
The head was small, often very small, with slender antennae com- 
posed of numerous segments. The eyes were large and conspicuous. 
The mouthparts were haustellate, forming a prominent beak, re- 
sembling superficially that of the Hemiptera. However, the head 
was not opisthognathous but clearly hypognathous, perhaps with a 
tendency towards the prognathous condition: the beak is preserved 
in the fossils in front of the head, projecting somewhat obliquely in 
an anterior-ventral direction. Four long stylets were included in 
the beak, their basal portions being covered by a triangular or 
lanceolate labrum. The clypeal region was markedly swollen and 
enlarged, much as in the Hemiptera, and possessed a median longi- 
tudinal ridge as well as several transverse ridges. It seems almost 
certain that this enlarged clypeal region marked the presence of a 
sucking pump. The stylets were apparently held tightly together 
but were probably moveable, to some extent. The palpi, presumably 
the maxillary pair, were slightly longer than the beak and were 
attached to the head laterally at the base of the beak. The palpi 
were segmented, six segments being present in specimens in which 
the details can be ascertained; the first segment as well as the last 
one or two segments were much shorter than the others. The surface 
of the palpi was rugose. The beak itself was from 2 to 2.5 cm long 
in the moderate to large Palaeodictyoptera although in one such 
species (Lycocercus goldenbergi) the beak was only 1 cm long. In 
smaller specimens, such as some spilapterids, the beak was corre- 
spondingly shorter. 
The thoracic segments were nearly equal in size, though the 
prothorax was frequently somewhat shorter and sometimes narrower 
than the others. A median, longitudinal ridge was often present. 
