124 DISCOVERY REPORTS 



Similarly the known range of salinity is from 34-08 % to 35-33 % . 



From data given for 179 'Meteor' hauls where Dimophyes arctica was taken I have computed 

 a known range of salinity 34- 14-36-57 % , and of temperature 0-14-22-05° C. 



The data given on pp. 125-126 are representative, but not good enough perhaps, for drawing very 

 definite conclusions. To do that it would be necessary to examine a much larger number of catches, 

 and especially ones taken at all times of the year, such as those taken at full stations on the meridians 

 of o° and 20° E. 



New records of catches o/D. arctica in the Indian Ocean {i.e. north of subtropical convergence) 



The data indicate that D. arctica has a much greater range of tolerance than Diphyes antarctica, 

 or at any rate that the habits of the two are quite different, for it would seem that the differences in 

 their geographical distribution are mainly brought about by their resorting to different depths at 

 various times, or at different stages in their life cycle, for this would bring them into currents which 

 flow in different directions at various depths. But Mackintosh (1934) did not find any marked diurnal 

 variation in the catches of the N 100 B nets, and there is probably little diurnal migration up or 

 down of the polygastric stages upon which Mackintosh worked. 



On 17 November 1952, after this report was prepared, I received from Dr Fraser of Aberdeen 

 some siphonophores taken in June of this year, and amongst them an undoubted posterior nectophore 

 of Dimophyes arctica taken in a horizontal tow at 20 m. at ' Scotia ' Station 1 199. The temperature and 

 salinity recorded at that depth were 12-05° C. and 35-39 % . 



Bigelow & Sears (1937, fig. 81) plotted the frequency of capture of certain siphonophores, including 

 D. arctica in ' Meteor ' hauls in Atlantic water of known minimum and maximum temperature. The 

 main distribution for D. arctica was from 2° to 14° C. with a maximum around 3 C. At the sixty 

 ' Discovery ' Stations mentioned on p. 125 the most frequent occurrence was between — i° and 6° C, 

 with a very small marked maximum between i° and 2° C. (Text-fig. 64). 



