TETRAPLATIA VOLITANS 



139 



Detailed hydrographic observations were not made at the North Atlantic stations; those for the 

 South Atlantic are plotted on Fig. 5. Here Tetraplatia is an inhabitant of Sub- Antarctic water 

 and of the South Atlantic Central water at temperatures between 1-39° C. and 5-07° C. However, at 

 St. 2641 in the Equatorial Atlantic, Tetraplatia was taken in a haul from 100 m. to the surface, where 

 the temperature at 50 m. was aa-yy" C. The species must therefore be considered eurythermal. 



Hydrographic data are available for only one catch from the Pacific (Fig. 6). This was St. 943 to 

 the south-east of New Zealand where the species was found in W. S. Pacific Central Water. 



Fig. 7. Distribution of Tetraplatia volitans in relation to density layers. Each point represents the probable temperature 



and salinity at depth of capture as in Fig. 5. 



In the South Atlantic, Tetraplatia has been found in salinities of 34-i4%o-3477%<, and at St. 2641 

 on the equator where the salinity at 50 m. depth was 36-08 %o. Tetraplatia must thus be regarded as a 

 euryhaline species. 



The distribution of Tetraplatia volitans in relation to salinity, temperature and density is plotted 

 in Fig. 7.* 



To conclude, therefore, Tetraplatia can exist in temperatures of 1-39° C.-2277° C, salinities of 

 34-i4%o-36-o8%o and densities of between (o",) 24-83 and 27-85, so that the species can be regarded 



* .St. 2641 from the Equatorial Atlantic where the temperature was 22-77° C., the salinity 36-08 %„ and the density 24-83 

 at 50 m. depth cannot be plotted on this chart. At 100 m. depth the temperature was 16-85° C.; the salinity 35-72 %o and 

 the density 26- 1 2. 



