GENERAL NOTES 219 



BlRAPHIDINEAE. 



Generally speaking the Biraphidineae were very poorly represented. Among the six 

 species of Navicula observed, two deserve especial note. N. lyra Ehrenberg was ob- 

 served in material from St. WS 622. Only a few specimens were found, and they dif- 

 fered in no way from those found around the coasts of Britain. This is the first time 

 that this diatom has been recorded from the Antarctic. N. membranacea Cleve was found 

 at St. 1373, off the coast of Natal. This peculiar form is a weakly siliceous Navicula, 

 possessing considerable development in the zonal aspect, and characteristic strap-like 

 chromatophores. It is a neritic form favouring a fairly high salinity. Two species of 

 Amphiprora were observed, A. Kjellmani at St. 440, off the coast of Natal, and A. 

 Oestrupii, a cold-water form, found in water obtained from melted ice. The former is 

 found quite frequently in northern waters. In the subfamily Nitzschioideae the genus 

 Nitzschia was represented by four species. N. seriata was very widespread, particularly 

 in the more southerly waters where it existed in enormous quantities. N. closterium also 

 occurred but was never abundant. 



DIVISIONS OF THE FLORA 



The examination of the phytoplankton from so many different and widely spread 

 localities has made it possible to review the various diatom floras that inhabit the 

 southern seas. For the sake of convenience they will be dealt with in the order sum- 

 marized below. 



Two main floras are recognized and are controlled by the climatic conditions under 

 which they exist. These are subdivided into groups, similar to those used by Gran, 

 based upon the habit or mode of living adopted by the species. 



(1) Warm-water flora : (2) Cold-water flora: 



A. Oceanic: A. Oceanic: 



(a) Holoplanktonic. (a) Holoplanktonic. 



B. Neritic: (b) Special: 



(a) Holoplanktonic. (i) Parasitic. 



(b) Meroplanktonic. (ii) Adventitious, 

 (r) Tychopelagic. B. Neritic: 



(a) Holoplanktonic. 



(b) Meroplanktonic. 

 (r) Tychopelagic. 



Before considering the subdivisions in detail the general construction of the two floras 

 will be examined. Naturally these floras are not exactly distinct, and the intermingling 

 which takes place in the transition areas makes it very difficult to define their range 

 clearly. They have not been defined by the hydrologically determined convergence lines, 

 but in the main the boundary between them will be found to coincide with the sub- 

 tropical convergence. The floras must be considered in relation to the ocean currents 

 that support them more than in relation to the actual degrees of latitude through which 

 they spread. It is found that the flora of any given area varies from another in the same 

 latitude, if the two areas are separated by any appreciable number of degrees of longi- 



