REPORT ON THE ISOPODA. 145 



last species ; the anterior three pairs are attached close to the anterior border of their 

 segments, the two middle pairs close to the middle, and the posterior pair at the posterior 

 extremity of its segment. 



The abdomen is one-fifth of the length of the thorax ; the first segment is rather 

 longer than the three following, which are subequal, the segment is about equal in length 

 to the first. 



The antennules are more slender and shorter than the antennae, and are much 

 shorter than the head ; they are four-jointed, the basal joint being the longest and 

 stoutest ; the three distal joints are subequal in length but diminish progressively in 

 width. 



The antennae are shorter than the head but considerably longer and stouter than the 

 antennules. The basal joint is excavated in the same fashion as in Parantliura chiltoni 

 in the stoutest and largest joint ; the following joint is extremely short, the two follow- 

 ing longer, the more distal being the longer of the two ; the terminal joint of the 

 appendage is short and narrow and bears a dense tuft of hairs at its free extremity. 



The thoracic appendages are specialised in the usual way, as in the last described 

 species for example. 



Station ] 49h, off Cumberland Bay, January 29, 1874, Kerguelen ; depth, 127 fathoms ; 

 volcanic mud. 



Family Sph^eomid^:. 



There is perhaps no family of the Isopoda in which the makers of new species and 

 genera have run riot to the extent that they have in the Sphseromida? ; and the explana- 

 tion of this is that the sexual dimorphism of many species is so pronounced that the 

 males and females have often been assigned to different genera. So very many species 

 and genera have been described, and in many cases so imperfectly, that it becomes a matter 

 of the greatest difficulty to discriminate between new species and those that have already 

 received a name, if not an adequate description. The family is evidently in need of a 

 revision ; but since this would be beyond the scope of the present work, it is hoped that 

 in criticising the following new species the difficulties attending the study of this section 

 of the Isopoda will be borne in mind. 



Gerstsecker in his account of the Isopoda, in vol. v. of Bronn's Klassen und Ordnun- 

 gen des Thierreichs, has associated together many genera regarded by naturalists, or at 

 least regarded by some naturalists, as distinct ; he includes within the genus Sphwroma, 

 Zuzara, Cycloidura, Isocladus, and refers Dynamene to Cymodocea and Cilicwa to 

 Nesaea ; with this alteration I thoroughly concur, but would further associate Nessea and 

 Cilicasa with Cymodocea ; the chief distinction between the two former genera and the 

 latter is in the form of the uropoda, and I shall have occasion to show, in the course of 



(ZOOL. CHALL. EXP. — PART XLVIII.- — 1886.) Bbb 19 



