302 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



divided by two longitudinal grooves the Branchio- 

 cardiac grooves (It. (jr.) — into a median Cardiac region 

 (Card.) and two lateral branchial regions. Each branchial 

 region is made up of an anterior Mesobranchial region 

 (Mb.) and a posterior Metabranchial region (Mtb.) and a 

 small inner Epibranchial region (Kb.). 



The ventral inflected portion of the carapace is 

 divided into two parts by a well denned groove, which 

 may be termed the pleural groove, as it probably marks 

 the separation between the cephalo-thoracic terga and 

 pleura. It is along this groove that the carapace splits 

 during ecdysis (see section on Ecdysis). The pleural 

 groove commences at the epistoma and passes outwards 

 and slightly backwards until it almost reaches the 

 posterior end of the seventh lobe of the antero-lateral 

 border. Here it turns backward and runs parallel to the 

 postero-lateral ridge, finally reaching the posterior border 

 with which it becomes continuous. Thus the pleural 

 groove divides the inflected portion of the carapace into 

 an outer, or Sub-hepatic region, and an inner, or Sub- 

 branchial region. The sub-hepatic region may be 

 considered as an inflected portion of the tergum, and the 

 sub -branchial as belonging to the pleural region. Milne- 

 Edwards regarded the sub-branchial region as part of the 

 cephalo-thoracic epimera, but the inner walls of the 

 branchial chambers undoubtedly represent the epimera. 



2. Pre-oral Cephalo-thoracic Sterna. 

 (PL III, figs. 19, 20.) 



Yentrally the median lobe of the rostrum passes 

 backwards as a triangular plate, the apex of which points 

 posteriorly. This plate, which is separated at its posterior 

 end from the first sternum [antennulary sternum] (S 1 ) 



