130 Sellards — Structure of Paleozoic Cockroaches, 



triangular, pointed extensions of the meso- and meta-thoracic 

 terga, equal in size and of a similar texture. The pronotum 

 at this stage is abruptly truncated at its posterior margin. The 

 abdomen is slender ' and long. The sterna of the specimen 

 are partly exposed. The most remarkable feature in the 

 fossil, giving it an especial interest, is the presence near the 

 end of the abdomen of two pairs of organs and traces of a 

 third, which appear to represent the parts of the ovipositor 

 not yet united (Figure 11). These lie at a level below the 

 edges of the terga and the cerci, but above that of the sterna. 

 The stage of development of the ovipositor represented by this 

 specimen is very similar to that of the young Locusta illus- 

 trated by Dewitz {hoc. cit.). A later stage in the ontogeny of 

 the species is represented by Figure 13. The wings are now 

 directed obliquely backward, and are more arched. The dor- 

 sal integument of the abdomen is here entirely removed from 

 the seventh sternum and ovipositor and from the rest of the 

 abdomen except at the edges. The parts of the ovipositor 

 have now become united, the line of union being indicated by 

 a furrow. The ovipositor is seen to pass on the inner side of the 

 large seventh sternum, and is incomplete, being broken at the 

 tip. The part preserved is 3 mm long. The opposite side of 

 the nodule shows the ten segments of the abdomen complete, 

 together with the cerci. The sterna of the slightly larger 

 individual shown in Figure 12 are also partly exposed. On 

 the inner side of the seventh is what appears to be the 

 ovipositor lying at a lower level and passing beneath the 

 tenth tergum. The abdomen has suffered lateral crushing 

 in fossilization so that the sterna are displaced to the right and 

 the ovipositor lies almost under the right cercus. Figure 14 

 rep resents one of the larger specimens of this species. Besides 

 the thorax and wings, the head and two legs are preserved. 

 On the head can be seen the outline of the two rather large 

 eyes. Toward the front of the head are two small paired 

 bumps and between these a smaller elevation. A line at the 

 top of the head divides the epicranial plates. The pronotum 

 at this stage has rounded angles, a full posterior border, and 

 overlaps the base of the front wings. A pair of elevations 

 is seen close to the median line and near the front of the 

 pronotum. A second pair is placed farther back and out 

 from the median line. The pits observed by Schuchert on 

 Mylacris (DipeltisJ diplodiscas are doubtless of the same 

 nature. The front and hind wings are as yet scarcely differen- 

 tiated from each other either in size or texture. They are 

 still united to the terga by their entire base, although a thick- 

 ened spot, represented in the drawing, indicates the place at 

 which the articulation of the wing is forming. A delicate 



