1969] 
Kukalovd — Palaeodictyoptera 
471 
short distance. To avoid confusion and to emphasize the postcostal 
position of this area, I changed (1964) the term to postcostal area 
and pointed out its probable homology with the so-called costal brace 
of Ephemeroptera. 6 The interesting and intermediate condition 
between the well developed triangular postcostal area and its com- 
plete reduction and replacement by the precostal area is present 
in Dictyoneuridae. In this family, which has a broad precostal strip 
and which is very probably related to Eugereonidae and Calvertielli- 
dae, there is only one weak postcostal vein, oriented along the wing 
axis and ending usually on Sc, recalling the costal brace of the may- 
flies more than structures in other Palaeodictyoptera. 
The origin of the costal hrace-postcostal area probaly goes back 
to the common ancestors of Palaeodictyoptera, Megasecoptera, 
Diaphanopterodea and Ephemeroptera. The strongly developed 
costal brace has been found in aquatic Permian mayfly nymphs 
(Kukalova, 1969) probably helping to support the obliquely oriented 
and independent wing pads. In adult Permian mayflies the costal 
brace was less developed than in the nymph and probably non- 
functional. On the other hand, the terrestrial (apparently) nymphs 
of Megasecoptera (Carpenter, 1969) and Palaeodictyoptera (un- 
described material from Westphalian, Illinois) have a vestigial post- 
costal area very much as in the adults. It is possible that in ancestral 
palaeopterous nymphs there was a selective trend towards the ability 
to hold the wings in a more posterior position. The costal brace- 
postcostal veins possibly helped to hold the wings in this favorable 
position. 
The other striking morphological feature of the Eugereonidae is 
the presence of a deep furrow crossing the anal area obliquely and 
ending on the stem of M. It has been found in Dictyoptilus , 
Eugereon and very probably also in Peromaptera. This feature is 
best beveloped, though not unique, in this family and apparently 
developed independently in the very thin wings or very large wings, 
so-called, in addition to Eugereonidae and is most pronouncd in the 
Calvertiellidae (thin wings) and Homoiopteridae (very large 
wings). The fuction of this furrow is very puzzling, since the wings 
6 New and undescribed material of Calvertiellidae from the Lower Permian 
of Czechoslovakia shows beyond any doubt that in all known specimens of 
this family (including Calvertiella, which I had an opportunity to restudy 
recently) there is a well developed, large precostal area; the postcostal 
area is completely missing, as in the Eugereonidae. In this respect my 
account on Calvertiellidae (1964) has to be corrected. 
