An examination of one bottom sediment sample (NEL, 394) 

 revealed the following forms: Fragilariopsis antarctica; 

 Fragilariopsis antarctica f. bouvet ; Thalassiothrix longissima 

 var. antarctica ; numerous Coscinodiscus spp.; Charcotia 

 bifrons ; and spines of Chae'toceros, These are all very 

 robust, highly silicified forms and capable of passing unaltered 

 through the digestion tracts of "grazers." This probably 

 accounts for their presence in the bottom sediment. 



Methods . The investigation was carried out on semi- 

 permanent strewn-plankton mounts. The diatoms were washed 

 six times in distilled water. They were allowed to settle for 

 24 hours between washings and the supernatant water was 

 drawn off by means of a fine pipette and a vacuum pump. 

 After the final washing a few drops of the sediment were 

 placed on a slide and gently warmed until dry; a permanent 

 mount was then prepared. For a critical examination of the 

 species, a mountant with a high refractive index is necessary. 

 For this purpose Hyrax (a synthetic resin with a refractive 

 index of 1.71) was used. These preparations give excellent 

 results and last for many months. 



List of Species. The following is a list of the species 

 encountered. They are arranged in alphabetical order to 

 facilitate reference and the authority is quoted: 



Actinocyclus bifrons , Karsten,^ 1905, p. 92. 



Previously reported as common around South Sandwich 

 Island and South Georgia, this species occurred but rarely 

 in this collection. 



Actinocyclus janus, Karsten.H 1905, p. 92. 



Amphora peragallorum, van Heurck, 2 1909, p. 7. 



Asteromphalus brokkei, Bailey, * 1856, p. 2. 



Aste romphalus elegans , Greville,^ 1859, p. 161. 



Asteromphalus heptactis (Brebisson), Ralfs ex Pritchard,15 

 1861, p. §J8~ 



73 



