CKUSTACEA 93 



of seven segments. The segments of the head and thorax are 

 fused together ; these regions of the body are also fused and 

 protected by the cephalothoracic shield or carapace. The 

 thoracic portion of the latter is formed by an outgrowth of 

 the hinder region of the head fusing with the dorsal portions 

 of the thoracic segments, and it extends downwards on each 

 side to protect the gills. The distinction between the head 

 and the thorax is indicated by the cervical groove. The 

 cephalothorax is produced anteriorly into a rostrum armed 

 with three or four pairs of dorso-lateral spines, and one or two 

 median spines antero-ventrally, all of which are brought into 

 use during ecdysis ; the rostrum is fringed with hair-like 

 processes (setae) on each side. A depression on each side of 

 the rostrum receives the stalked movable eyes, which are 

 large and of the reniform shape which has suggested the 

 generic name. Branchiocardiac ridges provided with small 

 pointed projections divide the thorax into a median cardiac 

 region, and the gill-covers or branchiostegites. On both head 

 and thorax there is a median dorsal ridge bearing small points, 

 other depressions and ridges, and on the head there are series 

 of spines. 



The abdomen consists of seven segments, articulated to 

 one another at each side, and connected by thin uncalcified 

 portions of the integument. Each presents a beautiful regular 

 pattern produced by elevations and depressions, and each, 

 with the exception of the last, bears a pair of appendages. 

 The last segment forms the median element of the tail or 

 paddle, the other contributing elements on each side being 

 the modified and highly developed appendages of the sixth 

 segment. 



The limb-bearing segments of the abdomen each consist of 

 a dorsal strongly curved plate, the tergum, produced down- 

 wards on each side to form the two pleura, of a ventral sternum 

 between the appendages, and of the epimera between the 

 appendages and the pleura on each side. The pleura are 

 absent from the first segment. 



The females are smaller than the males, and in the female 

 the abdomen is broader, the pleura being more obliquely 

 placed. 



