152 



THE CRUSTACEA 



concealing, in most cases, the thoracic limbs. The two halves of the 

 shell can be approximated by the action of an adductor muscle 

 traversing the body in the region of the maxillae. Anteriorly, the 

 carapace is produced into a movably articulated rostral plate (r), 

 not provided with special muscles but elevated or depressed by the 

 movements of the underlying parts. The carapace is not attached 

 to the body behind the maxillary region, and the eight thoracic 

 somites which, except in Nebaliopsis, are very short and crowded 

 together, are all distinctly marked off by grooves on the delicate 

 integument. Of the abdominal somites the fourth alone may have 

 distinct pleural plates, or these may be altogether absent. The 

 telson (t) boars the two styliform or lamellar furcal rami (/) 



ad. 



FIG. 87. 



Ncbalin Iripcs, 9, from the side, a', antemmle ; a", antenna; afci, ah, first and sixth 

 abdominal appendages.; ml, adductor muscle of carapace ; /, caudal furca ; p, palp of maxillula ; 

 r, rostral plate ; t, telson ; 1,7, lirst and seventh abdominal somites. (After Glaus.) 



articulated with it and moved by special muscles ; the anus opens 

 between the rami towards the ventral side. 



Appendages. The antennules (Fig. 88, A) have a peduncle of 

 four segments bearing a flagellum of varying length and, external 

 to it, a movable scale. It seems probable that this scale represents 

 the outer ramus of the antennule of other Malacostraca, and the 

 occurrence of four (instead of three) segments in the peduncle is 

 paralleled in certain species of Tanaidacea. 



The peduncle of the antenna (Fig. 87, a") is apparently com- 

 posed of four segments, of which the last two are coalesced in 

 Nebalia and Paranebalia. Hansen recognises, in addition, a short 

 basal segment and another, very short, between the second and 

 third of the larger segments. The exopodite is absent. The 

 distal part of the endopodite forms a flagellum which, in the adult 

 male, may be nearly as long as the body. 



The mandible (Fig. 88, B) has a strong molar process; the 



