OF THE PAST. 215 



Phoraspis-like aspect and density of membrane. This novel 

 assemblage of species bridges over the distinctions between the 

 Palceoblattarice and Neoblattarice. We find, first, forms in which 

 the front wings are diaphanous, with distinct mediastinal and 

 scapular veins, and the anal veinlets run to the border of the 

 wing (Spitobfattina, Poroblattina) ; next, those having a little 

 opacity of the front wings, with blended mediastinal and 

 scapular, and the anal veins as before (some species of Neorthro- 

 blattina) ; then those with still greater opacity, with the same 

 structural features (other species of Neorthroblattina) ; next, 

 those having a coriaceous or leathery structure, blended 

 mediastinal and scapular, and anal veins falling on the inner 

 margin (some species of Scutinoblattina) ; and, finally, similarly 

 thickened wings with blended mediastinal and scapular, and 

 anal veins impinging on the anal furrow (other species of 

 Scutinoblattina). 



It is not alone, however, by the union of the mediastinal and 

 scapular stems that the reduction of the veins in the wings of 

 later Cockroaches has come about ; for in many mesozoic types 

 the externomediaii vein is blended with one of its neighbours, 

 while in others not only are the mediastinal and scapular 

 united, but at the same time the externomedian and interno- 

 median. 



As regards the other structural distinction between the 

 Pakeoblattarm and Neoblattarice the course of the anal 

 nervules there is much diversity, and very imperfect know- 

 ledge, since this very portion of the wing is not infrequently 

 lost, a fracture most readily occurring at the anal furrow. In 

 most of the mesozoic genera, the anal nervules, as far as known, 

 strike the margin ; but the larger portion of these show a decided 

 tendency to trend toward the tip of the anal furrow, as in many 

 modern forms. This feature can hardly be considered as firmly 

 established in mesozoic times, and the same genus, as Scutino- 

 blattina, may contain species which differ in this respect. 



A further peculiarity of mesozoic Cockroaches, already 

 alluded to, is their generally small size. The average length of 

 the front wing of palaeozoic Cockroaches has been estimated to 

 be 26 mm., that of the Triassic Palceoblattarice is about 16 mm., 

 while that of the mesozoic Neoblattarice is 12 '5 mm. One 



