1969] 
Kukalova — Palaeodictyoptera 
44 1 
were in the process of reduction. The number of branches varies 
within the several genera of Homoiopteridae, and twigs occasionally 
occur in related families, in which MA and CuA are generally 
simple. In my opinion the families Homoiopteridae, Breyeriidae, 
Graphiptilidae and Lycocercidae form a phylogenetic unit, in which 
the Homoiopteridae represent in many respects the most primitive 
series. It is to be emphasized that the simple form of CuA and MA 
does not necessarily represent the more primitive stage, as generally 
believed. This hypothesis was based by Handlirsch on the assumption 
that the most primitive Palaeodictyoptera were the Dictyoneuridae. 
However, this family, except for the arched ictyon, is a very advanced 
one, with venation very specialized and already reduced. Of course, 
it is very difficult to determine, in our present state of meagre in- 
formation of the body structures, which of the families has the most 
primitive features. The geological record seems to be indicating more 
and more that probably all the larger families of the Paleodictyoptera 
were present and already well developed at the base of the Upper 
Carboniferous and that their representatives evolved very little dur- 
ing the rest of that period. As a rule within the insects, the many 
morphological features of wing venation do not have equal signif- 
icance for classification in all families of the orders. The presence 
or absence of branches of MA and CuA appears to be more stable 
for the spilapterid group than for the homoiopterid group. 
A remarkable feature, present to a more or less extent in all 
homoiopterid specimens I have had occasion to study [ Homoioptera , 
Boltopruvostia , Amousus, Ametretus and Thesoneura\ , is the sclero- 
tized strip and tubercles strengthening the costal area. It is especially 
marked in the largest specimens of the family, i.e., in all species of 
Boltopruvostia and in Homoioptera gigantea. 
This family includes the largest species of Palaeodictyoptera 
known. The wings are of nearly equal length, the hind wings being 
somewhat the broader. In addition to the venational characteristics 
discussed above, the following should be noted : postcostal area large, 
with several branches included ; Sc long ; area of Rs small ; MA 
simple or with short branches; MP with several branches; CuA and 
CuP parallel to each other ; CuA with several short branches directed 
anteriorly (usually), CuP with several branches. 
Body structures: head small, with projecting eyes and large 
clypeus. Pro thoracic lobes with radiating veins and many cross veins, 
often with undulated margins. Legs longer than in Spilapteridae, 
with elongate tibiae. Abdomen unknown. 
