2i6 DISCOVERY REPORTS 



of the convergence. The numbers vary considerably, those in 80° W being very much higher than 

 those in 0°, while those in 90° E were very small indeed. It will be seen that the population in 90° E 

 appears to be split into two parts, but it is doubtful if this is of any great significance as the numbers 

 are relatively small, and if the species is patchy in distribution then the net at Station 2804, 250-100 m. 

 may have missed the patch which would have linked the populations. 



Table 3. The occurrence of S. macrocephala in the lines of stations d', 90° E and 80° W 



Number of 

 Line 



90 



80° w — ~ — 



S. macrocephala. This species does not occur in numbers suitable for giving a contoured section, 

 but in the lines under consideration it occurred at the stations shown in Table 3. It was not recorded 

 from 80° W (possibly it was not recognized), but it has been taken by 'Discovery II ' in the Western 

 Pacific (Stations 2736, 2738, 2825, 2826) and from the South Atlantic sector (Stations 1771, 1772, 

 i773> 1775' 1776, 17771 1805, 1807, 1808), so it seems likely that it also occurs in the Eastern Pacific. 

 The species occurs in the tropics and subtropics and extends to the region of the West Wind Drift, 

 though it is never present except in very small numbers in the Southern Ocean. It is rather more 

 frequent in the Subantarctic than in the Antarctic. 



The shallowest depth horizon at which it has been taken is 750-500 m., but this is exceptional. 

 Johnston & Taylor recorded two specimens from a depth of 100 fms. (64° 34' S 117° i' E), but this 

 must be regarded as a mistake in identification as no other specimens have been taken at such a shallow 

 depth. The species has been taken in nets down to 2400 m. but even in large (2 m.) nets at depths 

 below 1000 m. the numbers caught have been very small, and one must conclude that it is an 

 uncommon form in the Southern Ocean. 



E. hamata (Fig. 8). It is not possible to define the northern limits of the distribution of this species, 

 as it is one of the classic examples of bipolar distribution with tropical submergence. Its southern limit 

 is the Antarctic continent. Its upper limit in the Southern Ocean is the surface, though immediately 

 north of the subtropical convergence it is only found in deeper water. Its lower limit is below 1500 m. 

 though it becomes less frequent in deeper water than it is in the top 500 m. 



This species is by far the most abundant chaetognath in the Southern Ocean, and in all three 

 sections it is very numerous. The section in 80° W, however, shows the greatest numbers with as many 

 as 1275 specimens per 250 m. haul. The numbers in 0° are slightly less and those in 90° E least of all. 

 If this disparity in numbers is considered then it can be seen from fig. 8 that the pattern of dis- 

 tribution is essentially similar in all three lines. The maximum concentrations in each line are in 

 the top 500 m, and the species is abundant to this depth in both the subantarctic and antarctic zones. 

 The numbers decrease sharply at the subtropical convergence in 0°, and, although this decrease is 

 not evident from fig. 8B, in 90° E the actual numbers taken (see Table ^b, p. 227) fall off con- 

 siderably at Station 2802 which was evidently just south of the convergence in that meridian. There 

 is no fall off in numbers evident in 80° W but then the northernmost Station (1320) was probably 

 200 miles or more south of the convergence. 



