38 



anterior prolongation of the last pleuro-sternal muscle 

 chamber. 



The endosternite is almost vertical, but there is a 

 slight forward tilt. The endopleurite is slightly concave 

 on its anterior face, and its plane is slightly posterior to 

 that of the endosternite. The border of the endosternite 

 surrounding the sternal canal has a slight notch. Around 

 the foramen of the pleuro-sternal muscle chamber the 

 endosternite of this arthrophragm fuses in front with the 

 fourth endosternite (7.) and posteriorly with the sixth 

 endosternite. Similarly along the outer border of the 

 endosternite, above the apodemal foramen, this arthro- 

 phragm is fused in front with the fourth endopleurite (k) 

 and behind with the sixth endopleurite. 



The sixth thoracic arthrophragm (Text fig. 5, C.) 

 arises between the sixth and seventh thoracic somites. 



The endosternite is convex on its anterior face, and 

 its plane is inclined considerably forward. Its median 

 border is longer than in the previous arthrophragms. The 

 notch in the sternal canal is much more pronounced than 

 in the fifth arthrophragm. The upper border of the 

 sternal canal is bent posteriorly, and its inner tip becomes 

 fused with the upper edge of the median plate in the last 

 somite. The dorsal border is fused with the anterior (or 

 dorsal) edge of the last arthrophragm. In this way the 

 seventh endosternite is completely roofed over and cannot 

 be seen clearly until the sixth endosternite is removed. 

 As in the previous arthrophragm, there is a large foramen 

 in the dorsal region of the endosternite through which 

 the pleuro-sternal muscle chamber passes (m.). 



The endopleurite is very similar to that of the fourth 

 arthrophragm. At the junction of the endosternite and 

 endopleurite this arthrophragm fuses in front with the 

 fifth endopleurite (n.), and behind with the seventh endo- 



