328 DISCOVERY REPORTS 



This phase was observed in the South Atlantic Ocean, the Ross Sea, and the Weddell 

 Sea. 



"hispidum" phase. (PL VIII, figs. 7, 8.) 



This phase is portrayed by Castracane's species Corethron hispidum and Corethron 

 Murrayanutn. The cells are strongly siliceous and vary considerably in size. The per- 

 valvar axis may be only just a little longer than the diameter, or may be six or seven times 

 as long. As usual in Corethron the greater the diameter of the cell, the less is the con- 

 vexity of the valve. The valve possesses several short spines dotted irregularly over the 

 surface ; sometimes they are numerous and very prominent, but they may be much re- 

 duced, rudimentary, or absent. The spines are not furnished with terminal claws. The 

 bristles which surrounded the valve are strongly developed, but not very numerous. 

 Each bristle is somewhat flattened on either side of a central rib ; it is broad as it leaves 

 the valve-mantle, but tapers to a fine point, and is armed throughout its entire length 

 with coarse spines. The connective zone is usually composed of annular segments some- 

 times very clearly marked, but they may be indistinct. Some of the small and narrow 

 specimens were marked clearly with annular segments towards the centre of the con- 

 nective zone, but showed distinct imbricate scales towards the valves. 



This phase was observed but seldom and appeared to be confined to warm waters. 

 It was observed off the coast of Natal and between the Cape of Good Hope and Bouvet 

 Island. 



"hystrix" phase. (PL VII, fig. 1 ; pi. VIII, fig. 1.) 



This is the broadest phase of the species and that most commonly met with in the 

 northern hemisphere. It is portrayed in Corethron hystrix Hensen and Corethron 

 valdiviae Karsten. The phase is very complex and epiphases occur which make de- 

 lineation impossible. In the southern hemisphere, particularly in the sub-Antarctic 

 Zone, the strongly developed and relatively thick- walled specimens described by Karsten 

 exist in enormous quantities. The cells, which often attain considerable size, are usually 

 from four to ten times as long as they are broad. The valves are of varying degrees of 

 convexity and seldom constricted as they approach the connective zone. The valves are 

 furnished with a marginal circlet of long and well-developed bristles. The bristles are 

 usually half as long again or more than the pervalvar axis of the cell, and taper to a fine 

 point, making an angle of approximately 45 with the main axis of the cell. The bristles 

 are armed with very small spines. The valyes are furnished also with a corona of shorter 

 and much finer bristles or hairs which stand erect upon the valve margin, and are not 

 bent back in the same manner as the large bristles, but form a small cluster or tuft. 

 These fine hairs are furnished with stout terminal claws which act as coupling hooks, 

 uniting the cells into short chains. This corona of fine hairs may be present at one end 

 of the cell only. The connective zone is composed of numerous scale-like intercalary 

 bands, which are sometimes very difficult to see, and are often interrupted by hyaline 

 spaces. 



This phase is very widespread in the Southern Ocean and the South Atlantic, and was 



