GENERAL NOTES 217 



C. Murrayanum Castracane was observed at one station only, St. 461. This form is a 

 short stout one and the bristles are somewhat flattened and bear spines. The connecting 

 zone is composed of annular rings, similar to those of Coscinodiscns concinnus Wm Smith. 

 I consider this to be either an abnormality or a winter resting stage of the hystrix phase 

 and therefore synonymous with Corethron criophilnm. 



The family Rhizosoleniaceae illustrates a marked departure from the structure and 

 habits of the two foregoing families ; the claws and bristles which are so characteristic 

 of Bacteriastrum and Corethron are almost entirely absent, and altogether new struc- 

 tural ideas are developed. Extreme development of the girdle or connective zone takes 

 place, and the valve is reduced to a relatively small cap variously terminating in a spine. 



By the formation of short chains, interlacing or matting takes place, which allows the 

 organisms to adopt colonial habits, and so to maintain their position in the surface 

 layers of the ocean. The genus Rhizosolenia with few exceptions is entirely oceanic, and 

 equally represented in cold and warm waters. Considerable variation takes place within 

 certain species, particularly in the diameter of frustule, and this was very marked in the 

 case of R. hebetata. 



At few stations in the South Atlantic did members of this genus occur abundantly, 

 and with the exception of the aforementioned species and the almost ubiquitous R. 

 styliformis , few specimens were encountered until 45 S was reached. Below this lati- 

 tude the genus became more frequent, particularly in the Bransfield Strait and the 

 Bellingshausen Sea, where pure gatherings sometimes occurred. 



The following classification of Rhizosolenia, suggested by Pavillard (1925) has been 

 adopted. 



Inermes: valves truncated, without terminal spine. 



Affines: valves rounded, with short spine. 



Robustae: valves elongated, conical, with spine. 



Imbricatae: two rows of lateral intercalary bands, spine dorsal. 



Genuinae: two rows of dorsiventral intercalary bands, spines long or short. 



Squamosae : intercalary bands numerous, scale-like. 



In the Leptocylindraceae all attempts at producing spines, bristles or claws are re- 

 linquished, and the solenoid or tubular development reaches its highest state. The 

 valves are very indefinite and the connective zone is composed of intercalary bands. The 

 family is sharply circumscribed and the genera closely related. Considerably more 

 work on the family is required before the exact relationships are fully understood. 



Leptocylindriis was observed but rarely, and although a certain amount of variation 

 was seen in the specimens, all have been referred to L. danicus Cleve. 



In the genus Dactyliosolen two distinct groups have been recognized; the cold-water 

 group is typified by D. antarcticus. Under this specific name I have placed as synonyms 

 Karsten's species borealis and laevis, as I have found that the characters of the one 

 species often merge into the other upon the same specimens. For the same reason, in 

 dealing with the warm-water group, I have placed Karsten's species D. meleagris and 

 Peragallo's D. Bergonii in the synonymy of D. mediterraneus Peragallo. The cold-water 



