WING-VENATION OF THE PLECTOPTERA. 149 
(5) The clavns or anal area is a wholly convex area, and may carry from 
one to three convex anal A^eins, any of which may be branched or simple. 
Appljang these rules to a well-preserved specimen of Protereisma, such as 
the one figured in text-fig. '6, which Prof. Schuchert kindly allowed me 
to keep for study during the last two years, the archaic condition of the 
wing-venation is clearly shown in that the application of all five of the above 
rules can be made without any doubt or hesitation. The high ridge of E, 
can be found at once with the concave vein Sc lying anterior to it. At the 
base of the wing there is developed a sliort convex vein between Sc and the 
costal border. This must be considered as a true primitive costal vein, C, 
not a basal branch of Sc, since it is convex and not concave. Sellards (1907) 
has already shown how it forms a brace for the costal border, and has its 
bomologue in existing Mayflies. 
. T EXT-riG. 3. 
3 
Ci*ic 
Basal portion of fore-wing of Protereisma sp., Lower Permian of Kansas, considerably 
enlarged to sliow details of venation. Note the cnbito-median Y-vein having M. 
as upper arm, Ci.ii as lower arm, and M,5 + Cui as main stem. For lettering, 
see p. 162. 
We should next set about determining Cui, the anal furrow and the clavus, 
keeping the consideration of M and Rs until the last, as it is the limits of 
these veins which have been the chief trouble in the past. Again returning 
to our specimen of Protereisma, we find that the only vein which satisfies the 
conditions for Cuj is that which has previously been called lA, and that its 
concave branch Cuj can be clearly seen running in the anal furrow with a 
characteristic curve basally, and separating off from the rest of the wing 
a small, but quite distinct, convex clavus on which only convex veins are 
