GENERAL NOTES 211 



of its range. Information received from Mr John A. Long of Leeds, indicates that 

 A. Ehrenbergii has established itself at other points within the Antarctic Circle; Mr 

 Long has observed this species in material collected by Sir Douglas Mawson's expedi- 

 tion to Adelie Land. 



AULACOIDISCINAE and AULISCINAE 



Although no representatives of these suborders were found in the material examined, 

 they have been set down in the systematic arrangement in order to show the gradual 

 development of the frustule from the discoid to the biddulphioid form. The term 

 biddulphioid is used to designate forms which possess a structure similar to that of 

 species of the genus Biddulphia Gray. The term is rather ambiguous and is often used in 

 a wrong sense. Its use implies angularity of valve outline, production of processes, and 

 considerable development of the frustule along the principal or pervalvar axis. 



BlDDULPHINEAE. 



This is a very large suborder which is almost exclusively marine and, with few excep- 

 tions, entirely neritic. The genera are arranged in order of decreasing silicification of 

 the frustules, and as this advances there is a marked loss of the true biddulphioid cha- 

 racters and a tendency towards oceanic habits. 



Our knowledge of the biddulphioid diatoms has always been in a state of confusion ; 

 attempts have been made from time to time to establish some sort of order amongst the 

 species, but with little success. 



The difficulty lies chiefly in the position of the genus Triceratium Ehrenberg. This 

 genus was established in 1840; two species were described, T.favas and T. striolatwn, 

 the former being considered the type. Since that time, however, many additions have 

 been made to the genus, in fact over 800 specimens have received specific or sub- 

 specific names. The genus was originally framed to accommodate triangular organisms, 

 but gradually it came to include many polygonal forms which appeared to differ from 

 one another in no other respect than in the increased number of sides. For instance, 

 T. favus has been found with the number of angles varying from two to thirteen, and 

 many of these forms have been given specific or varietal names. It must be admitted 

 that the original generic description was rather ambiguous and led to the inclusion of 

 almost any angular diatom, forms which in fact differed so markedly from the type 

 species as to render the definition of the genus almost impossible. It would serve no 

 useful purpose to recite the history of the genus, or to debate the many unsuccessful 

 attempts that have been made towards simplification; all of them are well known to 

 workers in the subject. 



Prior to the commencement of my work upon the Discovery material I was engaged 

 upon a monograph of the genus Triceratium, the completion of which was delayed by the 

 present undertaking. Although the number of species of this genus observed in the 

 ' Discovery ' material does not allow all my recommendations to be exemplified, the main 

 ideas and changes in nomenclature that have been found necessary are given here in so 

 far as they apply to the species observed. 



