18 SCUDDER ON THE DEVONIAN 



the costal margin, but very soon divides into two main stems. These two stems I take to 

 be : the upper the main scapular branch, of which the transverse vein is the base ; the lower 

 the externomedian vein, amalgamated with the former at the base, the two being com- 

 parable, as will be shown further on, to the same nervures in the Odonata. The connection 

 of the main scapular branch with the veins preserved in the field beyond cannot be 

 directly traced ; but from the position of the latter the following account must be sub- 

 stantially correct. It runs in a nearly straight course to the middle of the apical half 

 of the wing, where from not following the arcuate course of the main scapular vein it has 

 diverged considerably from it ; here its straight course suddenly terminates, but it passes 

 to the same point on the apical margin (just below or at the apex), by a gentle arcuation 

 subparallel to but distant from the main scapular vein, with which it appears to be 

 nowhere connected by cross veins. This main scapular branch emits two basal and 

 several apical inferior offshoots ; the apical offshoots are thrown off at wide angles, at sub- 

 equidistant intervals from the arcuate portion of the main branch, the first at its bend 

 being abruptly and widely forked not far from its origin, the others being simple and the 

 interspaces apparently free from cross veins. The basal offshoots are probably thrown off 

 (their origin is destroyed) at a little distance either side of the end of the basal third of 

 the wing ; and, unlike the apical offshoots, certainly diverge at a very slight angle, and are 

 each similarly forked ; the first from the base is forked near its origin, and its upper fork is 

 again divided narrowly about half way to the margin, the general course of all the near- 

 vules of this basal offshoot being broadly arcuate. The other and outer basal offshoot soon 

 runs parallel to the main scapular branch, and is connected Avith it by a straight oblique 

 cross vein in the middle of the wing, where it forks ; a short distance further on a piece is 

 broken from the middle of the wing, and the part beyond is displaced a little with refer- 

 ence to it, and apparently folded a little so as to obscure the exact course of these forks ; 

 which seem to become involved with the fork of the first of the apical offshoots, with 

 which, as well as with each other, they are connected by weak, inequidistant, straight, direct 

 or oblique cross veins. 



The externomedian vein can be traced in all its parts, excepting an insignificant 

 portion of the tip of the outer of its branches; the main stem takes an arcuate 

 course, parallel to the basal offshoot of the main scapular branch, and terminates on 

 the lower margin just beyond the middle of the wing ; half way from the transverse 

 basal vein to the margin it throws off an inferior branch, which soon becomes parallel to 

 it (and where it becomes so is connected by a cross vein to the vein below) and, by an 

 interpolated vein, which appears as a baseward continuation of this inferior branch, to a 

 bent cross vein in the same interspace, just beyond the middle of the basal half of the 

 wing ; this cross vein is bent on the externomedian side of the interspace. The inter- 

 nomedian vein is compound, being broken at the lower extremity of the transverse basal 

 vein (before which it is not seen) into two compound branches, each throwing off a couple 

 of inferior curved offshoots to the margin, which are connected together by two sets of 

 cross veins,— one Ijelonging only to the nervures of the upper branch, and in continuation 

 of the direct cross nervure in the externo-internomedian interspace ; the other set cover- 

 ing both branches and broken, each succeeding vein being carried successively further in, 

 the general course of the whole series being across the middle of the internomedian 



