BULIMINIDAE 135 



in some of Sir Douglas Mawson's material and he has been so good as to send me 

 specimens for comparison. They are smaller than the Discovery examples. 



Genus Cassidulina, d'Orbigny, 1826 



283. Cassidulina laevigata, d'Orbigny (F 157) (SG 185). 



Eleven stations: 177, 180, 181, 196, 363, 386; WS 204, 469, 506, 507 a, 507B. 



Except at St. WS 204, where it is frequent but very small, this universally distributed 

 species is extraordinarily rare, often represented by a single specimen only. The few 

 stations at which it occurs are, however, distributed all over the area, and range between 

 160 and 4773 m. All the specimens are typical, though varying greatly in size, the best 

 and largest at Sts. 177 and 363. 



284. Cassidulina pulchella, d'Orbigny (F 158) (SG 187). 

 Three stations: 196; WS 204, 205. 



Frequent at St. WS 204, which is in the deep water of the Scotia Sea, depth 3328 m. 

 Very rare at the other stations. All the specimens were small. 



285. Cassidulina lens, sp.n. (Plate VI, figs, 17-20). 

 One station: 363. 



Test nearly circular, highly biconvex, with broadly rounded unbroken peripheral 

 edge. Five pairs of straight-sided chambers are exposed on each face, but are very in- 

 distinct except in young shells or balsam-mounted specimens, owing to the smooth 

 surface of the test, the sutural lines being absolutely flush. Aperture rather small but 

 normal, with incurved edges. Walls thin, distinctly perforate, very smooth, glassy when 

 young, becoming polished white and opaque in large or dead shells, and then showing 

 no external signs of structure. 



Diameter up to 0-50 mm.; thickness about 0-30 mm. 



Not uncommon in 329 m. oflF Zavodovski Island in the South Sandwich Islands, but 

 not seen elsewhere. It is a very distinctive form in the unbroken smoothness of its 

 outline and surface. 



286. Cassidulina crassa, d'Orbigny (F 160) (SG 188). 



Forty-three stations: 162, 164, 167, 170, 175, 177, 180, 181, 186, 195, 196, 200, 201-3, 363, 366, 

 383-7; Port Lockroy ; WS 204, 205, 383, 385, 389, 393, 469, 471, 474, 476, 481-3, 485-7, 506, 507 a, 

 507B, 552- 



Generally distributed over the entire area, but, except at a few stations, never a 

 dominant species. In the Weddell Sea and South Sandwich area it is frequent at St. 

 363, rare or very rare elsewhere, and always a small or very small type. In the South 

 Orkneys area it is very common and large at St. 167 ; common but small only at Sts. 162 

 and 201 ; common also, but both large and small, at St. 170; very rare and small at the 

 remaining stations. In the Bransfield Strait and South Shetlands area it is very common, 

 both large and small types at Sts. 195 and WS482; common and large at St. 175; 

 common and small at St. WS 383 ; frequent to very rare and always small at the re- 

 maining stations. In the deep-water stations of the Drake Strait and Scotia Sea, and in 

 the Bellingshausen Sea it is usually small and very rare, though there are exceptions. 



