210 PART II. SYSTEMATIC ACCOUNT 



The length of the body, in all likelihood, is not less than 60 mm ; the fore- 

 part of the body, including the cephalic lobe, is 1 mm long by 0-25 mm broad. 



The spermatophores are unknown, since both individuals appear to be 

 females. 



The walls of the tube are stout, elastic and so soft that they may be easily 

 cut with a sharp scalpel. At the same time the tube possesses the charac- 

 teristic whiteness which recalls those of S. vinculatum, S. frenigerum and 

 Zenkevitchiana longissima (pp. 203, 213 and 388). It is made up of regular 

 rings, consisting of a firm opaque white substance, and of narrow transparent 

 delicately pleated intervals (Fig. 108C). The longest tube is 15 cm long by 

 0-3 mm in diameter. 



The large protosoma, the single row of pinnules, the strongly developed 

 bridle and glandular belt, and the characteristic unsegmented white tube are 

 the most important features distinguishing Siboglinum cinctutum. For the 

 features by which it may be separated from S. vinculatum see under that 

 species (p. 206). 



Material: two females. 



Locality: the northwestern part of the Pacific Ocean to the east of 

 Hokkaido Island, Japan. 



Depth: 3420 m. 



[8A. Siboglinum cinctutum Ivanov var. subtile Southward (Fig. A109) 



Southward 1961b: 9-11, 21, Fig. 5. 



This variety was found by Dr. Southward in her re-examination of the 

 Siboga material and was originally included by Caullery (1914, 1944) in 

 his species S. weberi. The following description is by Dr. Southward (1961) 

 and is reproduced by kind permission of the author and the publisher, 

 E. J. Brill. 



"The animals are . . . incomplete and are up to 25 mm long, with a tentacle 

 over 4-5 mm long. The tentacle is not very thick, 50 to 80/л in diameter, and 

 it bears one row of fine pinnules, 120 to 150/a long. The cephalic lobe of the 

 protosoma is rather short and there is no pretentacular groove visible, but 

 behind the base of the tentacle there is a semi-annular groove on the ventral 

 side and a second semi-annular groove, also on the ventral side, before the 

 bridle (Fig. AX09A). The bridle is only slightly raised; its narrow brown keels 

 are joined in a point on the ventral side but separated by a small gap on the 

 dorsal side. There is a slight longitudinal furrow on the ventral side between 



