SYSTEMATIC ACCOUNT 299 



Cells united to form long, stiff and usually straight chains. Cells in girdle view rect- 

 angular, elliptical in valve view. Valve surface flat, or nearly so. Poles of the valve 

 slightly produced, bearing the long stiff bristles. The bristles of one cell fuse with those 

 of the neighbouring cell and proceed thus for a short distance, perpendicular to the 

 pervalvar axis, but soon separate and diverge in straight lines. The bristles of the lower 

 valve of a terminal cell are usually much stouter than the others ; they emerge obliquely 

 at first, but become bent towards the axis of the chain until they are almost parallel. 

 Most of the bristles bear very small puncta, particularly towards the extremities. The 

 foramina vary in shape and size according to the season, linear-lanceolate in the summer, 

 broadly elliptical in autumn and winter. Chromatophores : several rounded bodies, 

 usually six to ten. Diameter of valve, polar axis 30-80/x. 



An oceanic species having a wide distribution. Usually regarded as Arctic or sub- 

 Arctic, being recorded from the north Atlantic and all north European seas. It was 

 observed however in considerable quantities all around the coast of South Africa, in the 

 Brazil Current, and in the Peru Current. 



Observed at Sts. 261, 427, 428, 432, 433, 434, 435, 437, 438, 439, 666, 675, 722, 723, 

 1373; WS 700, 701, 703, 704, 706. 



Section Dicladia 



Chaetoceros Lorenzianum Grunow. 



Grunow, 1863, p. 157, pi. 5, fig. 13. 

 Hustedt, 1930, p. 679, fig. 385. 

 Karsten, 1906, p. 167, pi. 31, fig. 6. 

 Lebour, 1930, p. 128, fig. 93. 

 Chaetoceros cellulosum Lauder, 1864, p. 78. 



Cells united to form short chains, but often solitary, rectangular in girdle view. 

 Valves elliptical in outline, central area flat or slightly convex. Valve mantle usually 

 deep, connective zone narrow. Angles of valve slightly produced to the long stiff 

 bristles, which cross those of the neighbouring cells at the point of emergence, pro- 

 ceeding in straight lines from the cells, diverging slightly. Terminal bristles usually 

 stronger than the others, divergent. All bristles very slightly swollen in the second half 

 of their length, that is the length farthest from the cells, but the terminal ones more so. 

 Bristles punctate. Foramina hexagonal to elliptical. Chromatophores : usually eight to 

 twelve large plates. Diameter of valve in the polar axis 44-60/n. 



A neritic species, very abundant in warm waters. It was observed at many stations in 

 the Peru Current, sometimes in great numbers, often amounting to over 90 per cent of 

 the total. 



Observed at Sts. 666; WS 580, 594, 629, 640, 641, 642, 646, 647, 648, 649, 650, 709, 

 710. 



Chaetoceros buceros Karsten. 



Karsten, 1907, p. 390, pi. 44, fig. 1. 



