224 PART II. SYSTEMATIC ACCOUNT 



rapidly (Fig. 114//); then yellowish or dirty-brown rings appear, at first very 

 irregular and often incomplete (Fig. 1147). In the middle part of the tube the 

 rings become coarse, dark and regular, though the edges always remain 

 uneven. Just as in the rings, the clear spaces between them contain rather 

 coarse sparse transverse fibres. The rings vary in length, but are always 

 considerably less than (sometimes only half) the diameter of the tube (Fig. 

 1147). I n tne nm d part of the tube the fibrous structure disappears, the rings 

 become regular, and each splits into two secondary rings. The overall 

 length of the doublet thus formed is much less than half the diameter of the 

 tube (Fig. W4K). Still farther back the rings gradually become simple again, 

 instead of double, and turn pale (Fig. 114L). The terminal part of the 

 tube is delicate, transparent and structureless. The front filmy part of the 

 tube is up to 20 mm long; a more or less complete tube may be about 12 cm 

 long. The diameter near the front is up to 0-12 mm, but at the back of the 

 ringed section it reaches only 0-08 mm. 



S. pusillum is linked with 5". caulleryi and S. cinctutum by the arrangement 

 of the pinnules in one line and by the possession of two adjacent girdles, but 

 it is distinguished from them by the arrangement of the toothed platelets in 

 a single row, the development of their anterior group of teeth and by the 

 development of a post-tentacular groove. In the latter respect it recalls 

 certain species lacking pinnules, namely S. tenue, S. microcephalum, S. 

 hyperboreum and S. bogorovi. In the development of the double rings in the 

 hind part of the tube S. pusillum is like S. variabile and especially like 

 S. tenue. 



Material : some dozens of fragments of tubes, half containing animals. 



Locality: northwestern part of the Pacific Ocean, between Onekotan 

 (49°N 155°E) and the northern part of the Kuril-Kamchatka Trench. 



Depth: 5529 m. 



12. Siboglinum buccelliferum Ivanov (Fig. 115) 



Ivanov, 1960c: 5, 12, 18, 19, 96, 128, 134, 151, 160-3, 174, 186, 188, 197, 265, Figs. 

 87, 115. 



S. buccelliferum was taken in July, 1957, in the northern part of the Coral 

 Sea near Treasury Island in the British Solomon Islands, by R.V. Vityaz\ In 

 washing through the muddy silt taken by a dredge at a depth of 960 m a 

 few tubes of Siboglinum were found, amongst which were two brownish 

 ringed tubes of an undescribed species. Both tubes contained animals. 



The fore-part of the body is comparatively short, with a length to breadth 



