DESCRIPTION OF SPECIES 291 



lateral angle of the segment. The median spine is long, prominent and acute, and is 

 situated in the anterior part of the segment ; behind it the median portion of the segment 

 is slightly keeled, and a transverse curved ridge, produced into three acute, flat spines, 

 one in the median line and one on either side, passes across the segment at the level of 

 the angular process of the oblique ridge. 



Remarks. The appendages of this species have not been described; the following 

 notes are based on observations made on the type specimen: 



The antennule and the antenna have been described by Richardson (pp. 396-7), who, 

 however, has not observed the structure of the flagellum of the antenna. As in S. schythei, 

 Lutken, a series of delicate lamellar processes is arranged in a single row on the ventral 

 surface, near the posterior margin of most of the joints— these processes are sHghtly 

 smaller than those present in 5. schythei. 



The basipodite of the maxilliped is fused with the lamella as in S. schythei (Fig. 2 b) : 

 it was impossible to see whether or not the extra minute joint of the palp was present. 



The second thoracic appendage is modified in the usual way; the propodus bears 

 modified spines of the types shown in Fig. 4 c. The third appendage (Fig. 4 d) of this 

 specimen has not developed the characters of the adult male. It is, however, stouter and 

 shorter than the remaining thoracic appendages, and bears a row of toothed spines along 

 the propodus ; the dactylus is modified in a similar way to the corresponding appendage 

 of S. schythei (Fig. 4 a). Long plumose setae, similar to those found on the pleopods, 

 are present on the posterior border of the ischium and at the posterior distal angles of 

 the merus and carpus of this and the remaining thoracic appendages (Fig. 5 e). 



Each of the sternal plates of the first three abdominal segments has the median pos- 

 terior border produced into a spine. The protopodite of each of the first three pairs of 

 pleopods is characterized by the absence of plumose setae; in this they agree with 

 S. schythei and S. paradoxa. 



The suture of the exopod of the fourth pair is oblique and the distal extremity of the 

 endopod is bifid, with the inner branch extended some distance beyond the outer; the 

 endopod of the fifth pleopod has a rounded distal extremity. 



The uropoda (Fig. 5,/) do not extend to the tip of the terminal segment; the exopod 

 is shorter than the endopod, both are broadly rounded, toothed, and fringed with plumose 

 setae. 



Distribution. South Sandwich Islands. 



This species is undoubtedly very closely related to S. schythei, Lutken, and also to 

 S. paradoxa, Fabricius. The following points result from a comparison of the three 

 species : 



(i) The males of 5. schythei are proportionately broader than those of the other two 

 species, whilst the body of the former is more flattened than that of the other two. 



(2) The head of S. polaris and S. schythei is broadest at the level of the eyes, whilst 

 that of S. paradoxa is broadest anteriorly. The eyes of S. schythei are larger than those 

 of S. polaris. 



(3) In all three species the first four free somites are separated by sutures from their 



