362 MRSOZOIC INSECTS OF QUEENSLAND, vi., 



somewhat cultriform area is separated from the rest of the 

 tegmen by a deeply impressed vein, called the vena dividens (vd). 

 This vein, in the Comstock-Needham system, must be either Cu 2 

 or 1A; but, as it does not seem to be quite clear, as yet, which 

 of these it really is, it is best to keep to the non-committal name 

 still in use with students of the Blattoidea. The anal area itself 

 is more or less convex, and hence it is usually very well preserved 

 in fossils, making a deep impression on the rock, much as a 

 Coleopterous elytron does. 



The veins supplying the anal area are termed either anal veins 

 or axillaries (Text-fig. 29, A); we shall adopt the former term. 

 In the Palaeozoic fossils, they all spring from the base, and take 

 a more or less oblique course towards the posterior border; none 

 of them ends upon the vena dividens. The same is true of most 

 Mesozoic fossils, though occasionally one, or perhaps two, of the 

 more anterior ones may be found to end up on the vena dividens, 

 just above the apex of the anal area. Recent forms with the 

 same condition still exist; but there are also many forms in 

 which, as in the one figured in Text-fig. 29c, the anal veins dis- 

 tribute themselves alike equally to the vena dividens and the 

 posterior border, or even run mostly longitudinally to the former 

 only. 



We may add to this account that, in the great majority of 

 Carboniferous fossils, there is a delicate close network of cross- 

 veins all over the tegmen; this is apparently a specialisation from 

 the older and more irregular palseodictyopterous meshwork, or 

 archedictyon, found in the Palseodictyoptera, Protorthoptera, and 

 Protoblattoidea. Intercalated veins are very rarely developed 

 In the Mesozoic fossils, on the other hand, intercalated veins are 

 often well developed, while the close network of cross-veins is 

 more rarely found. Most recent forms have the intercalated 

 veins well developed; and there still exist a number with the 

 cross- venation persisting, though it is seldom of so close a type 

 as in the Carboniferous forms. 



Thus, although the Blattoid type of tegmen has remained 

 remarkably stable through many millions of years, we are yet 

 able to see the general trend of evolution, as shown by the 



