214 DISCOVERY REPORTS 



The family Anaulaceae contains one genus only, namely Anaulus Ehrenberg. The 

 true position of the genus is most uncertain ; there is a suggestion of biddulphioid con- 

 struction, but it is not carried very far; there also appear to be certain pennate in- 

 fluences at work. One previously undescribed species was observed. 



The last family of this suborder, namely Chaetoceraceae, is very extensive, both as 

 regards the number of species observed and the number of organisms which occurred 

 in the hauls. Its position in the systematic arrangement is not at all clear and it probably 

 should not be included in Biddulphiineae. The family is confined to a marine habitat, its 

 members being both oceanic and neritic. It is probably of recent evolution as compared 

 with the Discineae. Considerable variation in certain species was observed, owing to 

 the habit of producing distinctly different summer and winter forms. These seasonal 

 forms were particularly evident in the more southerly samples, and it appears to be 

 likely that the seasonal changes are brought about to enable the organisms to maintain 

 their position in the surface layers of the ocean so as to make the most of the available 

 sunlight during winter months. 



The genus Chaetoceros has attracted the attention of many plankton workers during 

 recent years, including Cleve, Gran, Mangin, Pavillard, Ostenfeld, Meunier and Yendo. 

 The following classification based upon Gran's work in Nordisches Plankton (1905) is 

 taken from Lebour (1930): 



Subgenus Phaeoceros. 



Chromatophores numerous, penetrating into the bristles. Mostly oceanic. 



Sections: 1, Atlantica; 2, Borealia. 

 Subgenus Hyahchaetae. 



Chromatophores solitary or in pairs, but sometimes numerous, not penetrating into the bristles. 

 Mostly neritic. 



Sections: 1, Oceanica; 2, Dicladia; 3, Cylindrica; 4, Compressa; 5, Protuberatitia; 6, Constricta; 

 7, Stetiocincta; 8, Laciniosa; 9, Diadema; 10, Diversa; 11, Brevicatenata; 12, Curviseta; 13, Ana- 

 stomosantia; 14, Furcellata; 15, Socialia; 16, Simplicia. 



SOLENIINEAE. 



This suborder has received less attention than any other from workers in the past, and 

 is consequently little understood. The reason is twofold, first, that to the average worker 

 material containing the genera here represented is seldom available, and secondly, that 

 the inclusion of this important group of organisms under the so-called Centricae of 

 Schiitt, entirely robbed it of its individuality and obscured certain features of biological 

 significance. 



The arrangement of the families given in the systematic classification indicates a 

 gradual recession from gonioid forms to the truly solenoid. 



Apart from structural likeness in the main body of the frustule the Bacteriastraceae 

 bear certain resemblances to the Chaetoceraceae, particularly in the method of producing 

 resting spores ; but the complete circlet of bristles in Bacteriastrum is quite opposed to 

 the bipolarity of Chaetoceros. The circular section of Bacteriastrum led Lebour (1930) 

 to include it together with Corethron and Leptocylindrus in the Discoidae ; this, however, 

 I regard as an error. 



