E. H. Sellards — Types of Permian Insects. 255 



selves in the disposition of the cubitus. With the advanced 

 Anisoptera there is, as demonstrated by Needham, an abrupt 

 bend in the cubitus just back of the arculus, the bend thus 

 made forming the base of the triangle. With the Zygoptera 

 the bend is much less conspicuous and the sinuous or uniformly 

 curved type of Cu 1 is the rule. The Zygoptera have thus 

 retained a cubitus much less differentiated from that, of the 

 Permian form than have the Anisoptera. The course of Cu 2 

 in the Odonata is one of the highly characteristic peculiarities 

 of that unique order. Its distinctive feature lies in the fact 

 that immediately after leaving Cu 1 it fuses with the first anal, 

 continuing that vein and giving in the adult the appearance of 

 a single strong vein from the base of the inner border. In 

 those advanced Anisoptera in which the cubitus is most 

 abruptly bent, Cu 2 is given off at the point of closest approach 

 to the anal. With those more generalized Odonata in which 

 the cubitus has a sinuous course^ the basal part of Cu 2 appears 

 as a cross vein. It is hardly to be expected that the particular 

 cross vein representing the basal part of Cu 2 can in all cases be 

 recognized in the fossil genera. It is to be noted, "however, 

 that in the Permian genus Tupus a cross vein some distance 

 from the base becomes conspicuous by its strongly slanting 

 position (fig. 2). A similar slanting cross vein is seen in 

 Scudder's careful illustration of the Coal Measures genus 

 Paralogies* 



The characters thus far discussed are those which concern 

 the distribution of the main veins of the wing, and as such are 

 without doubt the structurally more important characters of 

 the wing. In these characters there is found to exist essential 

 agreement throughout between Paleozoic, Mesozoic, and mod- 

 ern dragon-flies. That there are differences, many and' obvious, 

 scarcely needs stating. Such differences as exist, however, are 

 associated almost wholly with the specialization of cross veins 

 and as such are of secondary importance. They are conveni- 

 ently discussed under the heading of cross veins. 



Cross veins. — Specialization of cross veins plays a leading 

 part in the development of mechanical strengthening devices 

 with which the wings of modern dragon-flies are so richly sup- 

 plied. With the Paleozoic dragon-flies, however, the cross 

 veins are but little differentiated among themselves. Such 

 specialization as has occurred has taken the direction princi- 

 pally of the matching of cross veins and is most advanced in 

 the basal and dorsal part of the wing. In the Permian genus 

 Tupus there is observed near the base a strong brace corre- 

 sponding to the triangular brace • at the base of the wing of 



*Bull. U. G. S., No. 101, pi. i, fig. a. 



