1886.] DURING THE VOYAGE OF H.M.S. 'CHALLENGER.' 'JP 



spinosum, and from the next species I. bacilloides. The specimen is 

 a female. 



Station 158 ; 1800 fathoms. 



2. ISCHNOSOMA BACILLOIDES, n. Sp. 



This species is closely allied to the preceding, but presents certain 

 differences which appear to necessitate its separation as a distinct 

 species. The single specimen is a fragment consisting of the same 

 segments as /. bacillus, save for the fact that the fourth segment of 

 the thorax is incomplete ; unlike the foregoing species, it is a male ; 

 hence the supposed specific difference may be sexual. This species 

 is to be distinguished from I. bacillus by the fact that the sixth 

 segment of the thorax as well as the fifth has a pair of lateral spines. 

 In both species the uropoda are simple, each consisting of two joints. 



Station 302 ; 1450 fathoms. 



3. IsCHNOSOMA SPINOSUM, n. Sp. 



This species is more closely allied than either of the foregoing to 

 Sars's two species Ischnosoma bispinosum and Ischnosoma quadri- 

 spinosum, and, like them, comes from the Northern Hemisphere. 



The single specimen measures 6 miliim. in length. The general 

 shape of the body is similar to /. quadrispinosum ; the head is 

 narrower and shorter than the first segment of the thorax ; there is 

 no trace of eyes. The first segment of the thorax is larger than 

 either of the two succeeding, which are subequal ; the fourth segment 

 is much longer and broader anteriorly than posteriorly, where it is 

 closely applied to the fifth segment, which is the longest of all ; the 

 sixth and seventh segments are short. The whole of the dorsal 

 surface of the thorax is roughened and tubercular ; the lateral 

 margins of the first three segments are furnished with two or three 

 longish stout spines, of which one on each side is particularly long ; 

 the dorsal region of these segments is not only tubercular but furnished 

 with a few longish spines ; the fourth segment has no long lateral 

 spines hke those of the preceding segment ; the remaining thoracic 

 segments have likewise no lateral spines. Between the thorax and 

 abdominal shield is a single free abdominal segment; the anterior 

 half of the latter is oval ; there is a deep notch behind this, just in 

 front of the articulation of the uropoda, which are borne upon a 

 short truncated process ; the extremity of the abdominal shield is 

 prolonged for some way behind the uropoda, and terminates abruptly 

 in a straight margin. The abdomen is roughened and tubercular 

 like the rest of the body ; there is a row of short spines on either side 

 of the dorsal median line. 



Station 78; 1000 fathoms. 



AsTRURUS, nov. gen. 

 This genus comes near to Plevrogoninn, Sars, but may be distin- 

 guished by the spiny body, the long bifid rostrum, and the long 

 epimeral spines, which are themselves covered with shorter spines ; 



7* 



