418 
Psyche 
[September-December 
Fig. 2. Palaeodictyopteran nymphal wing pad with partially separate 
basal plates. Idoptilus onisciformis (Graphiptilidae). After Wootton, 
1972, F — -deep furrow along the thorax; PI — basal plates. Westphalian, 
England. 
Palaeodictyoptera and Ephemeroptera 
In the most primitive, yet unknown, Paleoptera all main veins 
probably originated at the wing base from the separate basal plates. 
In the process of evolution, the basal plates gradually became fused. 
The intermediate stage of partial fusion is documented in the primi- 
tive palaeodictyopteron, Boltopruv ostia nigra (Namurian 'C of Czech- 
oslovakia, fig. i ) . In this species the subcostal and radial plates are 
fully grown together (forming the subcosto-radial plate), the median 
plate is separate, and the cubital plate is fused with the small anal 
plate (forming the cubito-anal plate). The partially separated basal 
plates are also indicated in the wing pad of the nymph Idoptilus 
h onisciformis (Wootton 1972, Westphanian of England) (fig. 2). 
Within the evolutionary history of Palaeodictyoptera, full fusion 
of the plates was acquired in the more specialized forms. Basal plates 
fused together into a single subcosto-anal plate but still retaining an 
indication of individual outlines, have been found in Moravia con- 
vergens (Lower Permian of Czechoslovakia, fig. 3). In Palaeodicty- 
optera from the Upper Carboniferous of France (fig. 4), the sub- 
costo-anal basal plate is fully fused and its subcostal part becomes 
reduced in size. 
In the primitive Ephemeroptera (Siphlonuridae, fig. 6), the costal 
brace in the fore wing starts at the anteroproximal angle of the 
axillary plate ; in the hind wing, it sometimes starts from a transverse 
elevation on the axillary plate, forming a convex hook directed against 
the stem of M. The costal brace is, in all probability, homologous 
to the postcostal vein of Palaeodictyoptera (fig. 4B, pv), plus the 
cross vein between Sc and R. The base of ephemeropteran wings is 
weakly sclerotized and the stems of the main veins adjacent to the 
axillary plate are mostly not discernible. However, if the vein stems 
