SECT. 4] 



BIOLOGICAL SPECIES, WATEK-MASSES AND CURRENTS 



391 



Thysanoessa gregaria 



Thysanoessa gregono 

 NORTH RAOFIC 



T riysonoesso gregono 

 SOUTH PACIFIC 



SUBANTARCTIC 



(b) 



Fig. 4. (a) The Pacific distribution of Thysanoessa gregaria within a transition zone between 

 central and subarctic (or subantarctic) water-masses. T-S characteristics of water 

 below about 150 m for the North Pacific habitat (b) and the South Pacific habitat (c) 

 of T. gregaria are compared with the T-S envelopes of the principal Pacific water- 

 masses. South Pacific T-S curves for the T. gregaria habitat are all from the eastern 

 half of the ocean. 



