44 



First thoracic arthrophragm (Text fig. 7, C). The 

 endosteruite arises from the upturned edge of the 

 sternum. It consists of a simple rod which passes back- 

 wards, upwards and outwards parallel to the articular 

 border of the second thoracic endosternite. It fuses with 

 the endopleurite of the same arthrophragm, but 

 immediately before doing so it comes into contact, on its 

 anterior side, with a posterior prolongation from the last 

 cephalic endopleurite (a.). 



The epimera of the first and second thoracic somites 

 are fused together, and the endopleurite of this arthro- 

 phragm arises from the ventral edge of the fused epimera 

 immediately in front of the origin of the second thoracic 

 endopleurite. It is rod-like, and passes forwards and 

 inwards in precisely the same plane as the first thoracic 

 endosternite, with which it fuses. Near its fusion with 

 the latter, the endopleurite gives rise to a posterior 

 process which fuses with the second thoracic endosternite. 



Last cephalic arthrophragm (Text fig. 7, B.). The 

 endosternites of the two post-oral cephalic arthrophragms 

 are fused together, but there is a distinct longitudinal 

 suture present, which assists in the identification of the 

 two parts.* The fused endosternites pass outwards and 

 backwards parallel to the first thoracic endosternite. 

 After a short distance the last cephalic endosternite 

 becomes distinct from the anterior endosternite, and at 

 the point of separation a prolongation from the first 

 cephalic endopleurite fuses with the endosternites (y. ). 

 From this point the posterior endosternite passes outwards 

 and fuses with the lower border of the last cephalic 

 endopleurite. 



The last cephalic endopleurite is an irregular 



:;: There is also a well-marked groove separating the sternum of 

 these two cephalic somites. 



