BY R. J. TILLYARD. 359 



The study of fossil cockroach tegmina is almost a special 

 branch of Entomology by itself, and has been brought to con- 

 siderable perfection by Scudder, Brongniart, Handlirsch, and 

 others. For the purpose of dealing adequately with the fossil 

 Blattoidea su far found at Ipswich, it would appear sufficient if 

 we indicated the typical venational scheme of a cockroach 

 tegmen, and pointed out the main lines of specialisation which 

 are shown in the evolution of this type of forewing, from its first 

 occurrence in the Upper Carboniferous, down to the present 

 day. 



Text-fig.29 shows three very typical cockroach tegmina, one 

 from the Upper Carboniferous of Europe, another from the Lias 

 of Europe, and a third from a still existing genus of Australian 

 cockroaches All three agree in the general shape of the tegmen, 

 though it may be said that the average breadth, in comparison 

 with the length, is greatest in the oldest forms, and decreases as 

 we pass up through the Mesozoic forms to those of the present 

 day. All three likewise agree in the very definite marking oft' 

 of a somewhat cultriform anal area or clavus. This character is 

 one of the most distinctive of the true cockroach tegmen, and 

 the area in question is generally excellently preserved in fossils. 



The differences between the three types are fairly obvious. 

 In the Carboniferous fossil, the subcostal vein (Sc) was well 

 developed, sending many branches to the anterior border of the 

 wing, and occupying at least half of that border. The only 

 space devoid of branch-veins is a small portion of the costal area, 

 at its extreme base, which we may term the humeral area (Text 

 fig. 29a, ha). The space lying between the anterior border of 

 the tegmen and the main stem of the subcosta, and including, 

 therefore, not only the humeral area proper, but also the whole 

 area supplied by branches of Sc, is the true costal, area (Text-fig. 

 29, ca). In the Mesozoic and recent types figured, the subcosta 

 becomes reduced to a simple vein, which borders the costal area 

 distally; and the latter becomes, like the humeral area of the 

 older type, free of branch-veins. There are, of course, many 

 Carboniferous types that show stages in this reduction; but they 

 are not dominant types for that period. Thus the Poroblattinidce 



