32 THE VOYAGE OF H.M.S. CHALLENGER. 



The telson (see fig. 12), as in the other forms belonghig to this family, is distinctly 

 developed, and defined from the last caudal segment l^y a well-marked transverse suture. 

 It is about twice as long as the last caudal segment and very narrow, almost linear, with 

 the base very slightly ddated to receive the terminal part of the intestine. Its distal 

 part is armed on each edge with a regular series of about ten denticles, the last of which 

 (see fig. 13) is much longer and stronger than the rest, and precisely of the same 

 appearance as the three apical spines, which are quite uniform in size. 



The uropoda (see fig. 12) are extremely slender and more than half as long as the 

 tail. The scape is considerably longer than the telson, narrow and cylindrical, with the 

 inner edge in the greater part of its length armed with a dense row of somewhat unequal- 

 sized spines. Of the terminal branches the inner one is the longer, nearly equalling 

 in length the scape, and composed of three distinctly defined joints, which are spinulose 

 at their inner edges. The first joint of this branch is by far the largest, being almost 

 twice as long as the two others taken together ; of the latter, the terminal is the smaller 

 one. The outer branch about equals in length the two first joints of the inner taken 

 together, and is only biarticulate, the first joint being very short, and the last slender, 

 and gradually tapering towards the tip, with a series of very delicate bristles on both 

 edges, those of the inner edge being more elongate. From the tip of this branch, more- 

 over, a somewhat stronger seta arises. 



Habitat.- — Numerous specimens of this form were collected on January 29, 1874, ofi" 

 Cumberland Bay, Kergueleu Islands, from a depth of 127 fathoms (Station 149h). A 

 sample of sifted mud from the same locality, kindly sent me by Mr. John Murray, also 

 contained, besides numerous small Amphipoda and Isopoda, several specimens of this 

 Cumacean, which thus seems to have occurred in great profusion at this place. 



Family IV. Leuconid.^. 



This family exhibits some very marked anatomical characters, distinguishing it from all 

 other known Cumacea. Thus the mandibles are quite peculiar in structure, and the other 

 masticatory parts also present certain well-marked diflerences from the usual structure. 

 Of the legs, the three anterior pairs in the female are provided with fully-developed 

 natatory exopodites, as in the Vaunthompsoniidte, but only two pairs of pleopoda are 

 present in the male. The tail in all the forms is very slender and highly movable, but 

 completely wants the telson, whereas the uropoda are powerfully developed. None of 

 the forms show any trace of an eye, and their habits would seem to be chiefly fossorial, 

 the second pair of legs having, in accordance therewith, an unusually strong develop- 

 ment. 



