go DISCOVERY REPORTS 



bars, and (3) the presence or absence of intermediate branchial papillae. In Table 28 I have shown 

 the variation in the ' Discovery ' specimens in respect of these three characters. A fourth character 

 which I have added is the presence or absence of a rib running forward along the inner siphonal wall 

 from the base of each tentacle (Text-fig. 27, rb.). This is a feature which I noticed in some specimens 

 and which is illustrated but not mentioned by Herdman (1923, pi. 13, fig. 1) in A. challengeri. Inspec- 

 tion of the way in which these characters are distributed among the specimens shows that it is im- 

 possible to maintain the distinctions made by Arnback in establishing A. dispar, which I therefore 

 regard as a synonym of A. challengeri. 



Table 28 



Two other species seem to be closely related, if distinct: A. placenta Herdman, and A. meridionalis 

 Herdman. Herdman (1923) himself suggested that A. meridionalis might prove to be the same as 

 A. challengeri. 



Distribution. Antarctic (South Georgia, Graham Land, South Orkneys, South Shetlands, Kaiser 

 Wilhelm II Land, Wilkes Land, King George V Land, Ross Sea), Subantarctic (Kerguelen). 



Ascidia interrupta Heller (Text-fig. 28) 



Ascidia interrupta Heller, 1878, p. 89, pi. 2, fig. 9. 

 For synonymy see van Name, 1945, p. 182. 



Occurrence. St. 279 : French Congo, West Africa, 58-67 m. 



External appearance (Text-fig. 28A). The three specimens are 7-3 cm. long by 3-0 cm. wide, 

 7-4 by 5-0 cm., and 7-6 by 2-8 cm. The shape is long and rather narrow, but the outline is irregular and 

 the surface of the body has swellings and depressions. At the anterior end the body is slightly narrowed 

 towards the oral siphon (o.s.). The atrial siphon (a.s.) is scarcely marked externally. It is situated 

 between one half and two-thirds of the body length from the anterior end. 



Test. The test is fairly thick, hyaline and cartilaginous in appearance, and is semi-transparent. 



Body wall. The left side of the body has few muscles, and on the right side the muscles form a loose 

 irregular, but mainly transverse, mesh of slender strands. When the test has been removed, the oral 

 siphon is seen to be a narrow, but not very long tube, and the atrial siphon a short conical tube pro- 

 jecting almost at right angles to the long axis of the body. 



Tentacles. There are from eighty to no oral tentacles in the 'Discovery' specimens. They are 

 slender and closely crowded. 



