REPORT ON THE ISOPODA. 39 



The uropoda are rudimentary ; each consists of a somewhat conical piece articulated to 

 the abdominal shield by its broad end; at the free extremity there are a number of long hairs, 

 and a minute articulated scale which appears to me to represent the endopodite; in figs. 16, 

 1 7 of PI. V. the terminal portion of this appendage is shown more highly magnified. 



Station 149k, off Christmas Harbour, Kerguelen, January 29, 1874; depth, 120 

 fathoms. 



Ischnosoma, G. 0. Sars. 



Isclmosoma, G. 0. Sars. Beretning om i Sonimeren, 1S65, foretagen Zoologisk Reise ved Kysterne af 

 Christianias og Christiansands Stifter. Christiania, 1866, p. 34. 



The Challenger collection contains two fragments of Isopods, which appear to belong 

 to this genus and to represent two new species of it, as well as a single complete specimen 

 of another species. 



This genus was formerly regarded by Sars as belonging to the Munnopsidas, but it 

 has since been removed by him to the family Asellidas. In his account of the Isopoda 

 collected by the Norwegian Expedition, Dr. Sars has pointed out that although the 

 general aspect of the Crustaceans belonging to this genus is not unlike that of the 

 Munnopsidas, the absence of any modification into natatory organs of the three posterior 

 pairs of thoracic appendages is opposed to their being placed in this family. The same 

 is also the case with Macrostylis. 



The genus is defined by Sars as follows : — 



Body elongate and narrow, broadest at first segment of thorax ; hinder part of 

 segment four and anterior part of segment five firmly connected, and forming an hour- 

 glass shaped portion which is nearly equal in length to half the body. Head small and 

 rounded, eyes absent. The abdominal segment much longer than broad, constricted at the 

 base, rather dilated towards the apex and obtusely rounded. Upper antennas projecting a 

 little beyond the first joint of the peduncle of the lower antennas, six-jointed, the second 

 joint narrow and elongated ; lower antennas slender, longer than the body, the flagellum 

 about ecpialling the peduncle in length and composed of about nineteen joints. Feet of the 

 first pair short and robust, subprehensile, the antepenultimate joint strongly dilated. Fol- 

 lowing feet slender and elongated, similar to each other, six-jointed, the last joint forming 

 a claw very elongate in the posterior three pairs of limbs. Caudal appendages simple. 



Sars has described two species of this genus, viz., Ischnosoma bisjoinosum and 

 Ischnosoma quadrispinosum ; the former is distinguished by the presence of a spinous 

 prolongation of the lateral margin of the first thoracic segment ; in Ischnosoma quadri- 

 spinosum, the first and fourth thoracic segments are thus provided, and the uropoda are 

 rudimentary. Two of the species to be described in the present Report are distinguished 

 in the first place by their very large size as compared with the two northern representa- 



