MAIN TYPES OF PHYTOPLANKTON 27 



"sea-sawdust" from Cook's sailors. It was, however, very definitely dominant among 

 the phytoplankton organisms taken at those stations. 



Elsewhere on the homeward passage, as we have seen, dinoflagellates in great variety 

 formed the majority of the sparse phytoplankton encountered in tropical surface waters. 

 The variety was so great, and the number of individuals so small, that it is difficult to 

 pick out any definite leading forms. The following species, however, occurred with some 

 constancy and in fair numbers : Ceratiim lineatmn, C. varians, C. ftisus, Ornithocerciis 

 magmficiis, and, towards the northern end of the line, Ceratium gibbenm f. sinistrum. 



The occurrence (in very small numbers) of Peridiniwn tripos at the most northerly 

 station on the line is of interest, as the only other recorded instance was at St. 677, south 

 of the tropical convergence. St. 699, in lat. 14° 27I' N and with a surface temperature 

 of 23-85" C, probably approaches the sub-tropical conditions of the northern hemisphere. 

 From this it would appear that this species may be found to be peculiar to sub-tropical 

 waters, as it was not present at any of the intervening stations. An interesting find 

 amongst the tropical phytoplankton was that of Richelia intracelhdaris epiphytic upon 

 frustules of Rhizosolenia styliformis at St. 693. 



The following is a list of all the phytoplankton species recorded from the stations 

 worked in tropical surface water on the homeward voyage, those peculiar to the tropical 

 Zone being printed in heavy type : 



Coscinodiscus spp. Ornithocercus magnificus, Stein 



Planktoniella sol, Wallich Goniodoma polyedricutn (Pouch.), Jorg. 



Asterolampra sp. Peridinium tripos, Murr. and Whitt. 



Hemidiscus {Euodia) cuneiformis, Wallich P. oceanicum, Vanh. 



Bacteriastnim varians, Lauder P- globulus. Stein 



Rhizosolenia castracanei, H. Perag. Peridinium spp. 



R. ? styliformis, Btw. Pyrophacus horologicum. Stein 



Chaetoceros ? didyinum, Ehrb. Ceratium candelabrum (Ehrb.), Stein 



Ch. peruvianum, Btw. C. lineatum (Ehrb.), Cleve 



Hemiaulus hauckii, Grun. C.fusiis, Ehrb. 



Gymnodinium (Pyrocystis) lunula f. lunula, C. bucephalum, Cleve 



Apstein C gibberum f. sinistrum, Gour. 

 Gymnodinium {Pyrocystis) lunula f. globulus, C. varians, Mangin 



Apstein C. limulus, Gour. 



Gymnodinium sp. Ceratium spp. 



Noctiluca scintillans. Macartney Podolampas bipes. Stein 



Phalacroma minutum, Cleve Pelagothrix sp. 



P. rudgei, Murr. and Whitt. Trichodesmium. thiebautii, Gomont 



Dinophysis schuettii, Murr. and Whitt. Richelia intracellularis, Schmidt 

 Amphisolenia globifera. Stein 



SUMMARY 

 The material collected on the long line of stations in 30° W afl^ords a basis for a com- 

 parison of the main types of phytoplankton met with in the South Atlantic, but owing 

 to the small number of the stations which fell in the sub-Antarctic and sub-tropical 

 Zones it has been necessary to take other work into account in dealing with them. 



