29 2 DISCOVERY REPORTS 



90 . Bristles short, stiff and straight, slightly inflated through the major part of their 

 length, but tapering to a sharp point. Valve mantle and girdle about the same depth, 

 defined by small constrictions at the points of juncture. Foramina somewhat large, 

 hexagonal. Chromatophores : numerous small bodies, which penetrate the bristles. 

 Diameter of valve, polar axis 20/*. 



Probably a neritic species, common in the Antarctic. It belongs to the C. atlanticum 

 group. It was observed frequently around South Georgia and Cape Horn. 



Observed at Sts. 378, 379, 380, 382, 460, 461, 477, 478, 505. 



Section Borealia 

 Chaetoceros boreale Bailey. 



Bailey, 1855, p. 8. 



Lebour, 1930, p. 117, fig. 83. 



Cells united to form short straight chains. Valves slightly convex, elliptical. Bristles 

 emanating from the valve surface above and within the valve mantle. Valve mantle 

 rather deep, straight. Connective zone very narrow. Bristles after crossing, tending to 

 be almost parallel. The bristles become thicker as they proceed outwards, and are often 

 covered with spines. Cells rectangular in girdle view, somewhat oblong, with the long 

 axis in the apical plane. Foramina distinct, but often narrow. Chromatophores: 

 numerous rounded bodies, penetrating the bristles. Diameter of valve, polar axis 

 30-48/x ; pervalvar axis 15-30/i. 



An oceanic species, with a wide distribution in subpolar and temperate seas of the 

 northern hemisphere. Observed in small numbers around South Georgia. 



Observed at Sts. 505, 509. 



Chaetoceros Glandazi Mangin. 



Mangin, 1910, p. 346, fig. 2. 

 Lebour, 1930, p. 118, fig. 84. 



Cells united to form straight chains, rectangular in girdle view. Valves almost circular, 

 with a slightly convex surface, bearing a small median process which meets and fuses 

 with the corresponding process of the neighbouring cell. Bristles long and straight, not 

 emerging altogether from the apices of the valve in the manner common to this genus, 

 but being more or less continuations of the valve surface, sweeping across the axis of the 

 chain from opposite sides. That is, when the chain is lying flat, the bristles on the right 

 side of the chain emerge from the left side of the cells, and those which appear on the 

 left side of the chain emerge from the right of the cells. The foramina are difficult to de- 

 fine, but appear diamond-shaped crossed by the median processes of the valves. The 

 bristles upon the lower valve of a terminal cell bear very short spines, the others are 

 plain. Chromatophores : numerous cocciform bodies, penetrating the bristles. Diameter 

 of valve 26/x ; pervalvar axis 34/1. 



An unmistakeable species, having a restricted distribution in temperate seas, prob- 

 ably neritic. Observed in small numbers off the east African coast. 



Observed at St. 1373. 



