XV111 



INTRODUCTION. 



< r A . 



The thorax in the Decapods in general is externally 



only visible under- 

 neath, the upper part 

 being covered by the 

 carapace, and being in 

 that part incomplete. 

 The number of obvi- 

 ous segments in these 

 higher forms is five, 

 and as each segment 

 bears its proper pair 

 of appendages, which 

 here are true ambula- 

 tory legs, the character of Decapods is thus produced. 



The superior surface of the thoracic 

 segments is limited to the epimera, 

 the tergum being absolutely wanting. 

 Upon this upper surface on each side 

 lie the branchiae, or gills. In this 

 brief sketch it is only necessary to 

 refer to the apodemata as consti- 

 tuting the large cells of the thorax, formed by a dupli- 



