2I 8 DISCOVERY REPORTS 



forms of this genus were frequently found associated with filamentous forms of Fragi- 

 lariopsis, particularly under neritic conditions. 



Araphidineae. 



The subfamily Fragilarioideae was by far the best represented in this suborder, which 

 contains littoral and oceanic forms. The most important forms are Fragilariopsis ant- 

 arctica, Thalassiothrix longissima and Thalassionema nitzschioides. The first two might 

 be considered as true oceanic forms ; they occur in enormous quantities, preferring cold 

 water and low salinity. T. nitzschioides occurred less abundantly and is a neritic and 

 temperate species. Fragilario striatula occurred occasionally between 34 and 43 ° S. 

 No difference could be observed between these specimens and corresponding specimens 

 found in European fresh waters. F. curia was obtained from melted ice taken near St. 

 560 in the Bellingshausen Sea, together with F. linearis. It is of singular importance 

 that this was the only station in which F. cnrta occurred. It is probably littoral around 

 the Antarctic continent. Licmophora Lyngbyei was another littoral diatom that occurred 

 frequently. This species is very widespread and occurs in enormous quantities in both 

 Arctic and Antarctic waters; it is also common around the shores of Great Britain. 

 Asterionella, another littoral genus, was represented by two species, both found off the 

 coast of Natal. 



MONORAPHIDINEAE. 



This suborder was poorly represented. The genera contained therein are in the main 

 littoral and belong to that group of diatoms generally referred to as the stipitate epi- 

 phytes. The cells adhere together, usually united valve to valve, to form short chains, 

 often enveloped in a strong mucilaginous coleoderm which may attach itself directly to 

 the substratum by a small cushion-like dilation or become attenuated to form a long 

 mucous stipe. The formation of the stipe gives rise to a frondose formation of the 

 colony. One outstanding exception to the general mode of living was seen in Cocconeis 

 ceticola. This must be regarded as an oceanic species and was found living singly upon 

 and within the cutaneous investment of certain species of whales. One species, C. 

 Wheeleri Hart (Hart, 1935, p. 259), was found only upon the Humpback whale, Mega- 

 ptera nodosa. Unfortunately I have not had the opportunity of examining this species, 

 and therefore have not included it in the systematic account. Of the genus Achnanthes 

 one species only was observed, namely, A. kerguelensis. This species was obtained at 

 St. WS481 in the Bransfield Strait, where the net touched bottom. Of the genus 

 Cocconeis, three littoral species were observed in addition to the parasitic C. ceticola 

 mentioned above. Two of these, C. pinnata and the beautiful C. imperatrix, were ob- 

 tained from the Bransfield Strait and also from shallow-water hauls made in the East 

 Cumberland Bay, South Georgia. It is probable that C. imperatrix is very common 

 around the coasts of the islands of the Southern Ocean, as examinations of deep-sea 

 oozes, taken in the neighbourhood of Tristan d'Acunha, indicated that an enormous 

 deposit of diatomaceous material was in the process of formation, and that C. imperatrix 

 was found frequently therein. 



