i6o DISCOVERY REPORTS 



Family RHIZOSOLENIACEAE, Schroder, 191 1 



Genus Rhizosolenia (Ehrb.), Brightwell, 1858 



Rhizosolenia alata, Btw. 



This ubiquitous and very variable species was very constantly present in all types of 

 Antarctic surface water, without ever forming any large proportion of the phyto- 

 plankton. It was also fairly frequent in sub-Antarctic water, and was encountered more 

 rarely farther north. 

 Rhizosolenia alata f. gracillima, Cleve. 



Mangin, 1915, p. 70, fig. 51 ; Lebour, 1930, p. 90, fig. 59. 



This attenuated variety was found to be very characteristic of the north-eastern 

 portion of the Bellingshausen Sea, and also of the north-easterly drift from that region 

 into the Bransfield Strait and the southern half of Drake Passage. In these waters the 

 more normal forms were rare or absent. 



Rhizosolenia antarctica, Karst. 

 Karsten, 1905, p. 95, pi. xi, fig. i. 

 A rare species observed at two spring stations in the old eastern Weddell Sea water 

 to the north-east of South Georgia, and at one station only to the westward in water of 

 Bellingshausen Sea origin. Present in moderate numbers at one station far to the south- 

 east in the Weddell Sea. 



Rhizosolenia bidens, Karst. 



Karsten, 1905, p. 98, pi. ix, fig. 13; Castracane, 1886, p. 73, pi. xxiv, fig. 14. 



Abundant at one station in eastern Weddell Sea water, to the south-east of the South 

 Sandwich Islands. Rare in the old water in the southern half of Drake Passage and on 

 the spring survey round South Georgia. Karsten concludes that this was the pro- 

 blematical form observed by Castracane. He himself figures the peculiar form assumed 

 by this species when in process of auxospore formation, but owing to the scale gives no 

 idea of its large size as compared with other members of the genus. 

 Rhizosolenia castracanei, H. Peragallo. 

 Lebour, 1930, p. 103, fig. 75. 



Observed at one station almost on the tropical convergence in 26° o6|' S, 30° W. 



Rhizosolenia chunnii, Karst. 



Karsten, 1905, p. 99, pi. xi, fig. 5. 

 This small Antarctic form, which typically occurs in long chains and closely resembles 

 the northern form R. faroense, Ostenf., was observed in the southern half of Drake 

 Passage in April, and was subsequently found to be of moderately frequent occurrence 

 in the Bellingshausen Sea. It was fairly abundant round South Georgia during the 

 spring survey, showing a maximum where the Bellingshausen Sea influence was 

 strongest. In the Weddell Sea area it was observed at two stations only, both in low 

 latitudes (57 and 59° S), in moderately large numbers. 



