vi INTRODUCTION 



description of any specimen mentioned. In these works 

 a number of names unfamiliar to the general public will 

 be met with which I have tried to do without by substitut- 

 ing, where possible, more familiar terms, or numbers. 



The following are the various parts to which the 

 reader's attention is drawn. 



The carapace, shell, " crab-back." The part that covers 

 the head and chest (cephalo-thorax) in one piece. It is 

 usually marked above with lines indicating the various 

 organs of the body lying beneath. Two lines passing 

 backwards and inwards, starting from the external angles 

 of the orbits, divide it into three portions ; one on each 

 lateral margin, one central. Of the regions on the lateral 

 margins, in front, is, on each side, the hepatic region, 

 covering the liver ; behind it the branchial region, 

 covering the gills. The central division is divided, from 

 before backwards, into, behind the orbits, the gastric 

 region, covering the stomach ; the genital region, covering 

 the organs of generation ; then a transverse line ; behind 

 tile transverse line the cardiac region, covering the heart ; 

 and behind this the intestinal region. On the front 

 margin are situated the eyes when present, usually pro- 

 tected by cavities, orbits, and placed on movable stalks. 

 The part between the bases of the eye-stalks is the frontal 

 region or front. The margin of the carapace is bounded 

 by an antero-lateral, a postero-lateral, and a posterior 

 border between the bases of the last pair of legs, where 

 the abdomen is attached. 



The abdomen may be large or small, covered with 

 a hard substance or with a soft membrane, divided into 

 segments or enclosed in a uniform sack, folded under the 

 body or extended backwards, and may be provided with 

 a terminal fan made up of expansions from the last 

 segment but one and the last segment (the telson), used 



