CALIFORNIA STALK-EYED CRUSTACEA. 



9 



The segments in some parts become fused together so 

 completely that the}^ manifest no external signs of 

 metamerism except the appendages they carry. The 

 five segments forming the head are usually thus indis- 

 tinguishably fused. The eight following segments, with 

 the rare exception of the last one, are fused together 

 and with the head, forming the cephalothorax; but the 

 sutures between the rings are, in this case, generally 

 visible on the ventral, or sternal surface and at the 

 sides. The abdomen is, in all cases, clearly marked off 

 from the thorax, and is typically composed of seven 

 segments. The number of joints may, however, be 

 secondarily reduced by the concrescence or disappear- 

 ance of some of the rings. 



The Carapace. — The carapace of the Decapod Crustacea 

 is considered to be a fold of the dorsal integument of 

 one or more of the cephalic segments which extends 

 backward over, and fuses with the dorsal portion of all 

 of the thoracic segments and is produced downwards at 

 the sides over the gills. The form of the carapace 

 commonly found in the Macroura is shown in the fol- 

 lowing cut: — 



^b.r 



Fig 1, — Macrouran Carapace, a. s, antennal spine; b.r, branchial region; c. g^ 

 cervical groove; h. s, hepatic spine; r, rostrum; s. o. s, suborbital spine; s. s, supra- 

 orbital spine. 



