94 DISCOVERY REPORTS 



At St. 461 very few specimens were taken and the vertical migration is not well denned, 

 but it is clear that this species lives at a considerable depth. 



Eiiphansia vallentini (Fig. 18). Since this really belongs to the sub-Antarctic water 

 there is not much material to go on. All that can be said is that there is a very definite 

 variation which seems slightly more marked than that of E. frigida. 



Thysanoessa spp. (Fig. 19). There is a clear diurnal variation, but it is not nearly so 

 marked as in Euphausia triacantha and E. frigida. Examples are taken just as often in the 

 middle of the day as at night, but the night hauls are on the average larger. At St. 461 

 Thysanoessa seems much scarcer in daytime, at all depths down to 600 m., than at night. 

 The variations at Sts. 618-25 are °f tne same order as those shown in the curve. 



Cleodora sulcata (Fig. 19). There is evidently a distinct variation. However, the species 

 occurs quite commonly in small or moderate numbers during the day. Three large catches , 

 which were evidently abnormal, have been disregarded in the construction of the curve. 

 There is evidence of vertical migration at St. 461, but no data from Sts. 618-25. 



Limacina helicina (Fig. 20). This species seems to be commoner at midday than at 

 midnight, but there is not a great amount of material and it is possible that the peak at 

 midday is accidental. The actual occurrences are distributed through the 24 hours as 

 evenly as could be expected. There is no definite evidence from St. 461 or Sts. 618-25. 



Limacina balea (Fig. 1 9). Like Euphausia superba, this species is difficult to place on 

 account of its patchy distribution and tendency to form shoals. The curve is constructed 

 from samples containing less than 1000. This represents the great majority of hauls and 

 shows quite a modest variation, but it is noteworthy that the catches of 1000 to 6000 all took 

 place at night, while two or three catches of 20,000 to 1 60,000 seemed to bear no particular 

 relation to the time of day. There is no definite evidence from St. 461 or Sts. 618-25. 



Spongiobranchaea australis (Fig. 19). Here the rather limited material suggests that 

 there is a slight variation, but the numbers of catches in which the species occurs are fairly 

 equal through the day. There are no examples at Sts. 618-25, and too few at St. 461 to 

 justify any conclusions. 



Clione antarctica (Fig. 19). The figures suggest a slight variation of the same order 

 as that of Calanus propinquus. There are few specimens but no indication of vertical 

 migration at St. 461. 



Salpa fusiformis f. aspera (Fig. 18). This is another of those species of which the vast 

 majority of specimens actually caught have been from a limited number of swarms. If 

 shoal catches are included in the calculation of the mean values for the different times 

 of day they produce an unfair distortion of the curve of variation. All samples of 100 or 

 more Salps have therefore been disregarded here, and the resulting curve shows a regular 

 and well-marked variation. If all samples of twenty or more Salps are also disregarded, 

 the shape of the curve is not much affected. There were not enough specimens at 

 St. 461 to provide additional evidence, and none occurred at Sts. 618-25. 



Chaetognatha (Fig. 19). The variations of the group as a whole are equivalent to 

 those of Calanus propinquus. Large catches are liable to be taken at all times of the day. 

 St. 461 gives inconclusive results, but there is a distinct variation at Sts. 618-25. 



