18 



The epimera of the third (mandibular) and the two 

 last cephalic somites (maxillary) are probably represented 

 by the membranous roof of the pre-branchial chamber at 

 each side (PL III, fig. 18, r.br.). This is continuous 

 behind with the thoracic epimera. 



5. Thoracic epimera 

 (Plate III, tig. 18, epm. 6-12). 



The thoracic epimera are represented by a continuous 

 plate at each side forming the inner wall of the branchial 

 chamber. This is the " flanc " of Milne-Edwards. The 

 lower border of the epimera commences immediately 

 above the base of the thoracic appendages. They pass 

 upwards and inwards and are continuous above with the 

 membranous roof of th^ branchial chamber. At the 

 posterior end they extend upwards almost to the carapace, 

 from which they are only separated by short muscles which 

 pass from the summit of the epimera to the carapace. At 

 the anterior end the epimera are much shallower and 

 become continuous with the roof of the branchial chamber 

 some distance below the carapace. 



The fused thoracic epimera form an extremely 

 convex wall Avhich is divided up into segments by vertical 

 sutures, which correspond to the lines of separation 

 between the various somites of the thorax. In this way 

 the epimera are divided up into seven portions. The 

 epimera of the first and second thoracic somites are 

 completely fused, and there is no groove separating them, 

 but apart from this there is one segment of the fused 

 epimera for each of the remaining thoracic somites. The 

 epimeron of the fourth somite is particularly broad. That 

 of the last thoracic somite is not bounded posteriorly by 



