326 



DISCOVERY REPORTS 



Cells usually solitary, but may be united to form chains. Cells cylindrical, length 

 (pervalvar axis) from one and a half to fifteen times as long as the diameter. Valves 

 circular, of varying degrees of convexity. Usually the convexity is greatest in the much 

 elongated cells, and in these the short valve mantle may show a weak constriction. The 

 valves are usually plain, but may bear a number of short spines or rudimentary granules. 

 The margin of both valves is usually furnished with a circlet of bristles, which are 

 directed towards the same pole, and make an angle from 30 to 65 with the pervalvar 

 axis of the cell. The bristles are straight or only slightly curved and taper to a fine point. 

 They may be plain or armed with small spines, they may be thin and hair-like or 

 flattened on either side of a central rib. 



The connective zone may be thick or thin, composed of a simple hyaline tube, or 

 numerous scale-like intercalary bands, or numerous annular segments. All combina- 

 tions of the above characters are often found upon the same specimen. Chromatophores : 

 numerous rounded or oval bodies, spread throughout the cell upon thin strands of 

 plasma. Nucleus central. 



Karsten described microspores. I have observed numerous inclusion bodies similar 

 to those recorded by Karsten, and identical bodies embedded in a mucilaginous film in 

 the Ross Sea. These bodies absorbed stain in the same way as nuclear substance. 



It would be impossible to express the size of the specimens of any phase by one set of 

 dimensions only, owing to the enormous range which was observed, and as the Corethron 

 population is without question the most important constituent of the South Atlantic 

 phytoplankton the opportunity has been taken to record several dimensions in order to 

 convey some idea of the size variation that exists in each phase. During this work several 

 thousand measurements of Corethron were made in an attempt to correlate the phases, 

 and it was found that the measurements of each phase could be arranged in an order of 



