3 o2 DISCOVERY REPORTS 



Chaetoceros pelagicum Cleve. 



Cleve, 1873 b, p. 11, pi. 1, fig. 4. 

 Gran, 1905, p. 83, fig. 101. 

 Hustedt, 1930, p. 704, fig. 402. 



Cells rectangular, small, united to form short straight chains, sometimes solitary. 

 Valves flat or nearly so, elliptical. The bristles emerge from the poles of the valve and 

 proceed in the direction of the axis of the chain to meet the bristles of the neighbouring 

 cells in line with the margin of the valve, then turning sharply outwards. Bristles long 

 and thin for the most part, slightly divergent. Valve mantle usually deep, connective 

 zone narrow. Foramina almost rectangular, usually as large as the cells. The bristles of 

 the lower valve of a terminal cell diverge slightly upon emerging, then continue almost 

 parallel with the axis of the chain, converging slightly towards their termini. Chromato- 

 phore: one small plate. Diameter of valve, polar axis 8-io/i. 



This species is often united with C. laciniosum, but I separate them upon histological 

 grounds. The species has a distribution similar to that of C. laciniosum. It was observed 

 at one station only off the coast of South Africa. 



Observed at St. 451. 



Section Diadema 



Chaetoceros breve Schiitt. 



Schiitt, 1895, p. 38, fig. 4. 



Gran, 1905, p. 83, fig. 100. 



Hustedt, 1928, p. 707, fig. 403. 



Lebour, 1930, p. 139, fig. 101. 



Chaetoceros hiemalis Cleve, 1900. 



Chaetoceros pseudobreve Pavillard, 191 1, p. 26. 



Cells united to form short chains. Valves often flat but sometimes with a central in- 

 flation. Bristles thin and often straight, arranged in the apical plane. Foramina elliptical, 

 sometimes almost square, but may be very narrow. Valve mantle usually equal to the 

 connective zone. Chromatophores : one large one in each cell, adpressed to the valve. 

 Diameter of valve, polar axis 20-26/x ; pervalvar axis 14-20/x. 



Common in the Atlantic and Indian Oceans. Observed frequently around the coast 

 of Africa. 



Observed at Sts. 425, 428, 433, 439. 



Chaetoceros Ralfsi Cleve. 



Cleve, 1873, p. 10, pi. 3, fig. 15. 

 Karsten, 1906, p. 168, pi. 33, fig. 16. 



Cells united to form chains, usually short, consisting of seldom more than six cells. 

 Valves elliptical in outline. Valve surface weakly concave with slight median inflation. 

 Bristles thin, emerging immediately from the angles of the cells. Those of the upper 

 valve are arranged in an almost horizontal position, while those of the lower valve pro- 

 ceed downwards in an oblique manner towards the posterior end of the chain. The 



