ZOOGEOGRAPHY 237 



Previous records. T. levinseni was collected by ' Discovery ' Investigations in the Antarctic and 

 Sub-Tropical Zones (Monro, 1930, as Sagitella kowalewskii and Travisiopsis sp., and Monro, 1936 

 as T. benhami), and Stop-Bowitz (1949, 1951) reported it from six localities in the Antarctic Zone. 

 The ' Meteor ' Expedition collected it in the South Atlantic but no details are available (Friedrich, 

 1950c). 



Pelagobia longicirrata 

 (Text-figs. 37-44, Tables 18 and 19, Appendices I and II) 

 The cosmopolitan P. longicirrata was collected in all explored water masses of the South Atlantic 

 except in the top 100 m. of Sub-Antarctic Surface Water between 45 S. and the Sub-Tropical 

 Convergence in the region of the Greenwich Meridian. This species rarely measures more than 

 12 mm. in length and was collected mainly by the N 50 and N 70 nets. 



In the surveys made about the Greenwich Meridian, P. longicirrata was found at all the stations 

 except two, Sts. 1774 and 1777 (Text-figs. \a and b); its distribution is shown in Tables 18 and 19, 

 and shows a concentration in the surface layers in summer and migration to depth in winter. It was 

 absent during July and August 1938 from hauls between 100 m. and the surface, and specimens were 

 only collected in this layer in June 1936 at St. 1782. From November to April, however, large 

 numbers of P. longicirrata occurred at almost every station between 100 m. and the surface. Below 

 100 m. the species was present at all depths throughout the year. This seasonal migration to depth is 

 similar to that which Mackintosh (1937) found in 8o° W. for the copepods Rhincalanus gigas and 

 Calanus acutus and the chaetognath Eukrohnia hamata. 



In the Sub-Antarctic Zone between the Antarctic Convergence and 45 S., P. longicirrata appeared 

 abundantly during the summer in the 100-0 m. nets, but north of 45 S. it was absent. Between 

 45 S. and the Sub-Tropical Convergence, ten nets were hauled in the November-April surveys 

 through 100-50 and 50-0 m. (two each at Sts. 2494, 2592, 2531, 2025 and 2026) and no specimens 

 were taken. Immediately south of Sts. 2494, 2531 and 2025, however, large numbers were collected 

 (forty at Sts. 2495, 470 at St. 2532 and fifteen at St. 2024). The salinity records at these stations show 

 that there is a difference of 0-52 % in the mean salinity of the top 100 m. of water between Sts. 2495 

 and 2494; that between Sts. 2531 and 2532 a difference of 0-42 % exists and between Sts. 2025 and 

 2024, 0-39 % . Each of these differences represents a greater change in salinity than that found in 

 crossing the Antarctic Convergence on the respective lines, the differences between Sts. 2496-2495 

 and 2535-2533 being 0-02 % and between Sts. 2022-2023, 0-04 % . Two of these changes in salinity 

 are indicated in Text-figs. 18 and 19 (pp. 211, 214) in which the isohalines in the region of the Antarctic 

 Convergence are almost horizontal, whereas at about 45 S. they rise almost vertically to the surface. 

 It is possible therefore, that, although the Antarctic Convergence does not restrict the surface dis- 

 tribution of P. longicirrata, a minor convergence may affect it in the Sub-Antarctic Zone, in latitude 

 45 S., and although cosmopolitan it may have a partially segregated summer population gathering 

 in the surface waters south of 45 S. for feeding and breeding purposes. 



The few records of P. longicirrata from the surface 50 m. of water around South Georgia (Text- 

 fig. 37) is in direct contrast to its abundance in this layer during the summer months on the Greenwich 

 Meridian. The species was not taken by any of the twenty-five nets hauled between 50-0 m. in 

 February-March 1928, and only eleven specimens were caught at three stations (309 (8), 338 (2), 

 and 334 (1)) in January-February 1930, although fifty-seven nets were hauled through the same depth. 



Hardy and Gunther (1935, p. 116) tabulated 459 specimens of P. longicirrata as being taken in 

 eighty nets from 50-0 m. At first sight this appears to indicate a widespread distribution of the 

 species in the surface layer; but reference to the basic data, given in Appendix II of their report, 



