E. H. Sellards — Types of Permian Insects. 251 



In the description to follow, the wing is considered by areas, 

 as in this way its relations to earlier and to later forms are 

 more readily indicated. 



The base of the wing. — The base of the modern dragon-fly 

 wing represents, as is well known, some yqyj characteristic 

 features. The costa is strong and marginal or with merely a 

 narrow expanse of thickened membrane. The subcosta lies at 

 the bottom of a deep fold. The radius and media are fused 

 at the base and lie at the top of a corrugation. The cubitus 

 appears in the basal part of the wing as a strong vein at the 

 bottom of a furrow. The anal, also a strong vein, lies in turn 

 at the top of a fold. Essentially the same features are pre- 

 sented by the base of the wing of Coal Measures and Permian 

 dragon-flies, thus affording a starting point in homologizing 

 the wing veins of Paleozoic and modern types. A clear recog- 

 nition of the homologous parts at the base of the wing is of 

 great importance in following the further interpretation of the 

 veins throughout the wing, and I introduce here for compari- 

 son the base of the wing of a modern dragon-fly with that of 

 the Permian form (figs. 2 and 3). 



The costa. — The costa, as indicated, is in essential agree- 

 ment with that of modern dragon flies. The genera thus far 

 made known from the Com men try Coal Measures have, 

 according to the illustrations of Brongniart, a more distinct 

 precostal area than has Tupus. The one genus known from 

 the American Coal Measures, Paralogus Scudder, in which 

 this basal area is preserved, has, according to Scudder,* the 

 subcosta (mediastinal) close to the margin. 



The subcosta. — The subcosta continues simple, reaching 

 usually beyond the middle line of the wing, gradually ap- 

 proaching and merging in the margin. In the modern forms 

 the subcosta terminates at the strong cross vein forming the 

 nodus. This special modification is concerned chiefly with the 

 specialization of cross veins and will be considered under that 

 head. 



The radius and media. — The radius and media sepa- 

 rate at a distance of from \\ to' 2 cm from the base, the 

 media going off at an oblique angle. Radius, continues as 

 a simple vein to the apex of the wing. The media 

 divides immediately after separating from the radius. The 

 two resulting divisions admit of interpretation as the homo- 

 logues of the veins marked in all of Needham's figures as 

 M T _ 3 , and M 4 , the upper division (M,_ 3 ) falling into a furrow, 

 the lower (M 4 ) topping a fold. Their subsequent divisions 

 likewise admit of homologizing in the same way. M 4 runs in 



* Insect Fauna of the Ehode Island Coal Field, Bull. U. S. Geol. Survey, 

 No. 101, p. 20, pi. 1, figs, a and 6, 1893. 



