Sellards — Structural Characters of Cockroaches. 315 



well-marked cross veins were entirely lacking in both wings ; 

 now, on the contrary, cross veins are numerous and not unlike 

 those of other Orthoptera. 



The plications are developed, doubtless, largely in response 

 to mechanical principles. Mechanical need, also, has probably 

 had an important influence in developing cross veins. The 

 interchange of circulating fluids in the wing, tending to follow 

 within established paths, may also, in some cases, have resulted 

 in the origin of cross veins. 



The writer is indebted to the kindness of Dr. S. W. Williston 

 for the opportunity of studying the collection of cockroaches 

 made for the University of Kansas Museum. Mr. Charles 

 Schuchert has very generously supplied valuable material for 

 study from the United States National Museum. Acknowledg- 

 ments are especially due to Prof. C. E. Beecher for assist- 

 ance in the study of Paleozoic cockroaches and in the prepara- 

 tion of the present paper. 



Yale University Museum, New Haven, Conn. 



EXPLANATION OF PLATES. 

 Plate VII. 



Figures 1-4. — Etoblattina mazona. The first specimen figured is nearing 

 maturity. Traces of the venation are seen, and a thickened 

 circular area indicates the place at which the joint of the wing 

 is to be formed. The tibiae, as indicated, are spinous. The head, 

 drawn enlarged in figure 2, is small. The eyes and a part of the 

 left antenna are preserved. The second specimen, figure 3, of a 

 younger stage, seen from the dorsal view, has the terga removed 

 except at the edges, thus exposing the sterna. The ovipositor is 

 seen to pass on the inner side of the enlarged seventh sternum. The 

 obverse side of the nodule shows all ten of the terga and the cerci. 

 From Mazon Creek, Illinois. 



Figure 5. — Etoblattina sp. The abdomen of this species is large. In the 

 flattened condition of the fossil the sterna show distinctly as 

 impressions through the terga. The lateral edges of the terga are 

 prominent. The specimen was obtained from the Upper Coal 

 Measures, at Lawrence, Kansas. 



Figure 6. — Front wing of an undescribed species from the Upper Coal 

 Measures of Kansas. Most of the anal veins end on the anal fur- 

 row, and the wing has numerous cross veins. 



Figure 7. — Hind wing from the Upper Coal Measures of Kansas. 



Figure 8. — Re-illustration of the type specimen of Mylacris (Dipeltis) cliplo- 

 cliscus. The relative distinctness of some of the structures is 

 necessarily exaggerated in the pen drawing. The head is com- 

 paratively large. 



Figure 9. — Moult of a Mylacrid nymph. The sterna with their pointed pos- 

 terior angles are seen as impressions through the terga. The 

 cerci of this species staud at right angles to the axis of the body. 

 Figures 8 and 9 represent specimens from Mazon Creek, Illinois. 

 Figures 1-7 are of the tribe Blattinarios ; figures 8 and 9 represent nymphs 



of the Mylacridae. Figures 2 and 4 are enlarged four times ; figure 8 is three 



times natural size ; all the others are twice natural size. 



Plate VIII. 

 Megablattina Beecheri, gen. et sp. nov. Twice natural size. 

 From Mazon Creek, Illinois. 



