SECT. 4] 



BIOLOGICAL SPECIES, WATER-MASSES AND CURRENTS 



389 



Distributions like that of E. pacifica are included in the subarctic group because 

 the centers of distribution are (1) subarctic water near the northern boundary 

 of the North Pacific Drift, and (2) upwelled subarctic water of the California 

 Current. 



A relationship between the distribution of the planktonic worm Poeobius 

 meseres and the subarctic water-mass was found by McGowan (1960). Though 



SUBARCTIC WATER 



SALINITY (%, 



Fig. 3. Temperature-salinity curves from the stations where Poeobius meseres was caught 

 during the "Transpacific" expedition, compared with subarctic and North Pacific 

 central T-S envelopes. Station numbers are indicated on the fine lines. Only that 

 segment of the curve within the depth range of Poeobius is plotted. (After McGowan, 

 1960.) 



widely distributed in the 150-300 m layer in the subarctic region, this species is 

 found at greater depths in the California Current and in the terminal part of 

 the Peru Current between 6°S and the Galapagos Islands (0°). Unlike Euphau- 

 sia pacifica, Poeobius submerges toward the southern limits of its range. The 

 tropical records were of specimens believed to be sterile expatriates : it was 

 implied that their occurrence near the equator might be due to a relationship 

 between eastern tropical intermediate water and subarctic water. 



