DESCRIPTION OF SPECIES 299 



Distribution. From 52° to 53° 53' S, and 60° to 63° W, between the Falkland 

 Islands and South America. 



This species appears to be most closely related to S. septemcarinata, Miers, and 

 S. glacialis, Tattersall. A comparison of these two species is included in the description 

 of the latter by Tattersall (1921, pp. 229-30) and certain points of difference are 

 noted. 



I have compared S. kempt with specimens of these two species in the present collec- 

 tion and have noted the following points of difference : 



(i) The body of S. kempi is broader in proportion to its length than in either of the 

 other two species: it is also less flattened. S. glacialis is more flattened, less compact 

 than S. septemcarinata and more transparent than either of the other two species. 



(2) The eyes of S. kempi and S. glacialis are larger than in 5. septemcarinata. 



(3) In S. kempt and S. glacialis each of the thoracic and first three somites of the 

 abdomen has the median dorsal posterior border produced into a spine-like process, 

 which is absent in S. septemcarinata. The spine of the third free thoracic somite in 

 S. kempi is much larger than any of the others and is also larger than the corresponding 

 one in S. glacialis, whilst those of the abdomen are proportionately larger in S. glacialis 

 than those of S. kempi. 



(4) In S. kempi the coxal plates of the seventh thoracic segment do not extend back- 

 wards as far as the pleural plates of the second abdominal segment, and these in turn 

 are shorter than those of the third abdominal segment. In S. glacialis the coxal plates 

 of the seventh thoracic somite extend backwards as far as the pleural plates of the third 

 abdominal segment and not quite as far as those of the second. In S. septemcarinata 

 the coxal plates of the seventh thoracic somite are shorter than the pleural plates of the 

 third abdominal segment, which in turn are slightly longer than or are equal to those of 

 the second. 



(5) In S. kempi the last segment of the abdomen bears anteriorly a prominent median 

 dorsal spine ; this is also present in 5. glacialis, but is absent from S. septemcarinata. 

 The median dorsal carina posterior to this spine extends to the tip of the segment in 

 S. glacialis, but ends in a short spine at some distance from the tip in S. kempi. There 

 are five dorsal carinae on this segment in both S. kempi and S. glacialis and seven on 

 that of S. septemcarinata. The posterior extremity of the segment is keeled and upturned 

 in S. kempi; it is trifid in S. septemcarinata, and is pointed in S. glacialis. 



(6) There are certain sexual differences which are characteristic of these species. In 

 S. kempi and S. glacialis the number of joints in the flagellum of the antennule is greater 

 in the male than in the female. Hairs are present on the merus, carpus and propodus 

 of the last thoracic appendages of the adult male of S. kempi and S. septemcarinata ; 

 these hairs are plumose in the former and simple in the latter species and are wanting in 

 S. glacialis. A further sexual character peculiar to the aduh male of S. septemcarinata 

 is the development, on the ventral surface of the second thoracic somite, of a row of 

 ridge-like tubercles, arranged in a semicircle with its convexity directed forwards and 

 outwards, situated one on either side just external to the articulation of the appendage. 



