REPORT ON THE ISOPODA. 87 



nearest to the latter species, but can be distinguished at a glance from either by the fact 

 that the spines are more numerous and more slender. 



One example was dredged at Station 153 close to the Antarctic ice barrier, being the 

 southernmost point at which the Challenger took soundings. 



The specimen is a female and measures 32 mm. in length ; the antennae were 

 unfortunately broken. 



The carapace is densely covered with short slender spines which extend on to the 

 thoracic appendages and uropoda. The spines are of ecpual length or nearly so, only a 

 few being conspicuously longer than the rest. 



The dorsal anterior margin of the head is excavated by a shallow semicircular notch ; 

 the lateral margin is straight and its lower angle is not produced into a spine as in 

 Arcturus furcatus. Between and in front of the eyes are a pair of long spines, inclined 

 somewhat outwards from each other, but not at so wide an angle as are the corresponding 

 .spines of Arcturus furcatus. Behind these the surface of the head is convex and bears a 

 single row of spines, of which the two on either side of the median line are considerably 

 longer ; in front is another band of small pointed tubercles. 



The first four thoracic segments are subequal in length and furnished with abundant 

 spines which are disposed as foUows in each segment ; the posterior part of the segment 

 is ridged as in so many other species, the ridge widening out laterally to occupy the 

 whole of the segment ; this ridge is everywhere closely beset with spines which even in 

 its narrowed sections are disposed in two rows ; laterally the number of rows of spines 

 is of course largely increased. On the anterior part of the segment, but some way from 

 its anterior boundary, is a slight ridge bearing a single row of similar spines. In all 

 except the first segment there are a pair of short spines between these two ridges, one on 

 either side of the median dorsal line. 



The epimera of these segments (that is, of the three posterior) are short, and so 

 covered by the tergum as to be invisible on a dorsal view ; their free margin is beset 

 with spines. As is so generally the case (cf. description of Arcturus spinosus, p. 89) 

 the epimera of the fourth thoracic segment are prolonged towards the median ventral 

 line into a long curved spine which supports the ovigerous lamella?. 



The three posterior thoracic segments decrease in length from before backwards ; the 

 first of them is conspicuously the longest ; each is ridged posteriorly ; the ridge widens 

 out laterally and comes to occupy the whole of the segment ; it is beset with spines 

 which, however, disappear at the dorsal median line. In the ventral median line the 

 first of these three segments has an oval convexity ; in the second segment this convexity 

 is also present and terminates anteriorly in a freely projecting sharp spine which is 

 directed forwards ; the third segment has tw T o such spines, one in front of the other ; the 

 anterior spine is directed forwards, the posterior backwards. Both Arcturus furcatus 

 and Arcturus spinosus differ from Arcturus glacialis in these respects {cf. the description 



