Sellards — Structural Characters of Cockroaches. 311 



character can be best observed on the two hind wings of the 

 type specimen of Promylacris rigida Scudder, the matrix 

 covering the borders having been removed for this study. 

 The wing is strengthened as in living forms by a deep fold 

 along the costal border. The area in front of this fold is 

 apparently broader in the Mylacridse than in the other tribe. 

 Cross veins, except for the wavy reticulation of the membrane, 

 seem to have been absent. 



Abdomen. — The seventh, eighth, and ninth terga of the 

 abdomen of Paleozoic cockroaches were evenly developed, at 

 least in all the nymph stages, presenting in this respect a 

 marked contrast to the common living forms in which the 

 corresponding terga of both sexes have undergone more or less 

 reduction. The lateral edges of the terga are well developed 

 and project freely from the edge of the body.* The sterna of 

 a number of specimens have been observed. They are seen 

 either as impressions through the terga, or, the terga having 

 been removed, are viewed directly. The seventh sternum of 

 the female is enlarged, rounded posteriorly, and has projecting 

 from beneath it (when viewed from the ventral side) a long 

 ovipositorf (Plate VII, figures 3 and 4). 



In the tribe Mylacridse the sterna in front of the seventh 

 resembles the terga in shape, being rounded in front and at the 

 anterior corners and pointed at the posterior corners (Plate VII, 

 figure 9). The corresponding terga of Etoblattina, and prob- 

 ably of most of the Blattinarise (with the apparent exception 

 of Spiloblattina) are, on the contrary, concave and pointed in 

 front and rounded at the posterior border (Plate VII, figures 3 

 and 5). 



The position of the eighth and ninth sterna of the female 

 has not been observed. In the recent cockroaches, however, 

 the first pair of ovipositors is attached to the eighth sternum, 

 which is reduced and telescoped within the seventh. Such 

 was doubtless the case, also, in the ancestors of these forms, as 

 indicated by the ovipositor passing on the inner side of the 

 seventh sternum. The double fold in the ventral integument, 

 which forms the characteristic genital pouch of the modern 

 cockroaches, seems therefore to have originated as early as the 

 Carboniferous, although the pouch could hardly have been so 

 perfectly developed at that time. 



Ovipositor. — The ovipositor is present on several specimens. 

 The parts of this organ in one very young individual of 



* Woodward has described a nymph from the Coal Measures of Scotland, 

 on which similar characters of the terga are noted (Geol. Mag., Decade o, 

 vol. iv, pp. 433-435, 1887). 



f The presence of an ovipositor on Paleozoic cockroaches was first noticed 

 by Brongniart (Comptes Eendus, Feb. 4, 1889, vol. cviii, p. 252), but has not 

 been previously observed on American specimens. 



