i66 DISCOVERY REPORTS 



south, also at the eastern end of Bransfield Strait from spring to midsummer, and still 

 later in the year at the Palmer Archipelago. Off South Georgia it shows a definite spring 

 maximum. 



Genus Hemiaulus, Ehrenberg, 1844 



Hemiaulus hauckii, Grun. 



Lebour, 1930, p. 183, fig. 143. 



Observed at three stations in the tropical Zone on the homeward voyage. Most 

 numerous at St. 679 in the immediate vicinity of the tropical convergence. 



Family EUCAMPIACEAE, Schroder, 191 1 

 Genus Eucampia, Ehrenberg, 1839 



Eucampia antarctica, Mangin. 



Mangin, 1915, pp. 58-64, figs. 41-4. 



Mangin has shown that the two species Moellerio antarctica, Castr., and Eucampia 

 balaustiiim, Castr., should be united, as he observed both forms and intermediates in 

 the same chains ; and he found that E. balaustimn was merely the winter form. Numerous 

 examples in our abundant material fully bear this out. The majority of the stations being 

 worked during the southern summer the moelleria form was naturally much the more 

 common of the two, and the long spiral chains to which Mangin assigns varietal rank 

 were observed only in spring. Our own view, subject to further investigation, is that 

 the torsion is a mechanical effect of the extreme length of the chains during the period 

 of rapid vegetative growth in spring. This species was abundant in all types of Antarctic 

 surface water, and particularly so on the spring survey round South Georgia when it 

 reached its maximum to the south-west of the island. Other regions in which it was 

 important were at the eastern end of Bransfield Strait up to mid-season, and at the 

 Palmer Archipelago even later. 



Family FRAGILARIACEAE, Schroder, 191 1 



Genus Fragilaria, Lyngbye, 18 19 



Fragilaria antarctica, Castr. 



Karsten, 1905, p. 122, pi. xvii, fig. 7. 



This is not the F. antarctica of Schwartz which should probably be referred to 

 F. striatula, Lyng., and not to Castracane's species as Karsten has done. 



One of the most important of Antarctic phytoplankton organisms. Abundant in all 

 types of surface water within the Antarctic convergence, more particularly in front of 

 the advancing ice-edge in spring and farther south later in the season. Principal con- 

 centrations observed: South Georgia (spring survey, south-west), south-west Bellings- 

 hausen Sea, Weddell Sea eddy in Bransfield Strait, and far south in the Weddell Sea. 



