1048 



CKUSTACEA. 



The cephalothorax has never a distinct cephalic segment, like many 

 Pontellae. The number of segments is usually four, one long anterior, 

 corresponding to all the anterior members, as far as the second pair of 

 natatories ; and then three short posterior, each bearing a pair of 

 natatories (the second, third, and fourth). Another segment posterior 

 to these is sometimes observed. 



The front has below a furcate beak, and in some species the furca- 

 tions are long capillary (Plate 75). 



The anterior antennae project laterally, usually with a double cur- 

 vature, the two bracket-like f - v^ ' ) in position, with the tips not 

 anterior to the line of the front. A few have the antennae straight, 

 and these form an approximation to the Pontellse. The number of 

 joints is large, and the setae are regularly arranged along the anterior 

 margin, excepting two or three upon the terminal joints, which project 

 backward. ' The relative lengths of the apical and subapical setae, as 

 well as the position of the antennae, afford good characters for distin- 

 guishing species. The subapical setae are those of the penult and 

 antepenult joints. 



The posterior antennae have each branch terminating in setae. In 

 the longer branch, the first joint constitutes the greater part of its 

 length ; the following part is quite short, and bears its setae in two 

 clusters. The shorter branch is nearly equal in its two joints ; the 

 setae at apex are three in number and they are bent; and besides these, 

 there are several longish setae on the side of the first of the two joints. 

 In a few species, the second joint consists of five or seven very short 

 joints. 



The organs of the mouth and their position are shown on Plate 75. 



The maxillipeds are like those of the Pontellae, but smaller. They 

 are straight, three-jointed, with several long setulose setae on the an- 

 terior side. 



The next pair of organs (the anterior legs) are long, and have a lateral 

 play, and the species are thus distinguished from the Euchaetae, m 

 which the five terminal joints are short, their setae collected into a 

 pencil, and the organs act only in the line of the body. 



The natatories have the branches either two- or three-jointed, 

 usually both the latter. 



The abdomen is without appendages, excepting the stylets at the 

 extremity. These are furnished with six setae ; the inner very short 

 (sometimes obsolete?), the next, which we have called the first (being 



