S. H. SCUDDER ON PALAEOZOIC COCKROACHES. 31 



exist; the second repeats the first, and the fourth the fifth, a little further removed from 

 the base, while the third vein, filling the space between the second and fourth, differs from 

 them only by its straightness and apical termination ; the general resemblance of each to 

 the others is very close. Yet one has scarcely more to do than to deepen the inner anal 

 vein, and perhaps remove the main veins a little nearer the costal border, giving a very 

 slight asymmetry to the wing, to impress upon such an ideal wing distinct blattarian 

 features ; for in all the palaeozoic cockroaches, partially excepting Oryctoblattina, the distri- 

 bution of the scapular branches more or less resembles that of the mediastinal, and that of 

 the internomedian the anal, while the externomedian branches occupy the middle ground 

 and the apex of the wing, seldom swerving to either side. 



It is, however, highly probable that such an ancient wing was broad at the base, for this 

 was the case with nearly all the palaeozoic insects, and certainly, which is more to our pur- 

 pose, with all the carboniferous cockroaches ; it is furthermore a characteristic of the cock- 

 roaches of the present day, and therefore all the more probably of high antiquity. In this 

 case the mediastinal and anal areas must have been more broadly triangular in shape than 

 the neighboring areas, and their veins consequently arranged in a more radiate fashion, the 

 different branches arising close together from a common base ; while in the neighboring 

 areas they would naturally arise at intervals from a main stem. This condition is precisely 

 that of the Mylacridae and would naturally precede that in which the mediastinal vein, to 

 strengthen the part of the wing most liable to strain, follows the basal curve of the costal 

 margin and throws its branches off at intervals toward the border, heightening at the same 

 time the resemblance between the distribution of the branches in the scapular and medias- 

 tinal areas ; a tendency to this appears in Necymylacris and it is fully developed in the 

 Blattinariae. That the anal vein has not followed the same rule is doubtless due, partly to 

 the small need of special support for the lower base of the wing, and partly to the deep 

 impression of the inner anal vein, which has forced, as it were, the other branches to ally 

 themselves with it. 



This view of the relative primitiveness of the two types of ancient cockroaches is 

 strengthened by noticing the further differentiation of the tegmina in modern times, where 

 the only remaining relic of repetition of characters in adjoining areas is the resemblance of 

 the disposition of the scapular and mediastinal branches; and even this resemblance recalls 

 the features of the Blattinariae. rather than of the Mylacridae. In all the Palaeoblatti- 

 nariae, so far as we know them, (excepting perhaps in Oryctoblattina,) the internomedian 

 veins have the same general tendency to repeat the downward ami outward curve of the 

 anal veins as we find in the corresponding veins of the costal region. But in recent cock- 

 roaches, not only do the anal veins run parallel to the inner margin and impinge upon the 

 anal furrow, but the internomedian veins may branch in any direction, so varied has the 

 plan of distribution grown ; in general however the internomedian vein may be said to 

 have assumed in modern types the role played by the externomedian vein in the Palaeo- 

 blattariae; and in not a few instances in the ancient types there is a marked tendency ot 

 both the scapular and internomedian veins, especially toward the .apex of the wing, to as- 

 sume a mode of distribution more closely resembling that of the externomedian than of the 

 mediastinal and anal branches respectively. Indeed the similiarity of the distribution of the 

 veins in the scapular and externomedian areas has induced me to place llermatoblattina 



