CRUSTACEA. i<> 



drical in form, and to be covered with a hard, limy 

 crust or shell. The body is divided into two clearly 

 defined parts. The posterior division, the abdomen 

 ( Fig. 6. a/>). which is nearer the pupils, has six distinct. 

 ring-like segments, and a terminal piece, all of which 

 are connected by soft skin, so that they move freely 

 upon each other. The anterior division (Fig. 6. cth) 

 docs not consist apparently of segments, and is called 

 the carapace, when referring to the visible shell alone. 

 ami eephalothorax, when the shell and the thorax in- 

 side are both spoken of, because the head and chest 

 appear to be in one piece. The carapace (Fig. 8. 

 A,C(i) terminates in a beak or rostrum anteriorly (ro), 

 on either side of which it is hollowed out to give room 

 for the eyes. One important feature of the carapace 

 ought not to be passed over. It will be noticed that 

 an incomplete suture or groove runs from a point near 

 the middle of the back of the shield downward and 

 forward towards the anterior end (fig. 6,su). This 

 suture, which doubtless many of the scholars think is 

 merely an accidental mark, is in reality of importance, 

 as will be seen farther on. when the true character of 

 the carapace is discovered. 



In order to arrive at this result, it will be essential 

 to study the appendages and the typical segment. 

 Turn the lobster upon its back, so that the ventral 

 surface, with all the limbs, may be exposed to view 

 (Fig. 7). 



It is best to begin the study of the appendages with 

 those of the abdomen, called the swimmerets. Each 

 one of these in the female is seen to consist of a more 

 or less flattened basal portion (Fig. <S. /:'. h i ), having 



