1886.] DURING THE VOYAGE OF H.M.S. ‘CHALLENGER.’ 99 
spinosum, and from the next species I. bacilloides. The specimen is 
a female. 
Station 158; 1800 fathoms. 
2. IsCHNOSOMA BACILLOIDES, 0. 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 J. 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 J. 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 millim. in length. The general 
shape of the body is similar to J. guadrispinosum; 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; tbe fourth segment has no long lateral 
spines like 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 Pleurogoniun, 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* 
