244 PART II. SYSTEMATIC ACCOUNT 



limp walls, is distinctly segmented and the boundaries between the segments 

 take the form of delicate, brown lines. Then gradually, in each segment, 

 three slight brown rings appear (Fig. 122G). The rings gradually increase in 

 length and become darker, until only narrow clear interspaces are left between 

 them. In this region the tube diameter is two and a half to three times the 

 length of the rings. The number of rings per segment appears to be inconstant, 

 and may be considerably more than the usual three. In one tube, indeed, there 

 were as many as nine rings per segment. Very soon the boundaries between 

 the segments begin to be irregular and the rings come closer together, so that 

 the interspaces are mere slits. In a short space the rings begin to anastomose 

 by means of narrow bridges or even to fuse in pairs, wholly or partially. The 

 walls of the rings increase considerably in thickness and the tube becomes 

 rigid (Fig. 133//). In the last third of the tube hazy, clear blotches appear in 

 transverse rows in the middle of each ring. Sometimes these run into one 

 another, thus dividing the ring into two narrower secondary rings (Fig. 1227). 

 Still farther back the edges of the rings become diffuse, the rings themselves 

 grow pale and the intervals between them longer (Fig. 122/), and finally the 

 rings disappear. The biggest fragments of tubes are 75 mm long; the diameter 

 varies between 1-12 and • 2 mm, but near the hind end it may be only • 1 mm. 



S. variabile is distinguished from related species also without pinnules 

 (S. tenue, S. bogorovi and S. hyperboreum), by the sharp division between the 

 protosoma and the mesosoma, by the swollen, ridge-like front edge of the 

 mesosoma, by the noticeable lateral and dorsal thickening of the keels of 

 the bridle compared with the thinner, ventral part, by the absence of any 

 groove immediately behind the base of the tentacle, by the possession of two 

 girdles of toothed platelets lying close together, by the weakly developed 

 anterior group of teeth on each platelet, and by the segmented tube. 



Material : about 20 fragments of tubes, some with animals. 



Locality: to the east of the North Island of New Zealand. 



Depth: 2072 and 3013 m. 



Substratum : calcareous clay and silty clay. 



19. Siboglinum bogorovi Ivanov (Fig. 123) 



Ivanov, 1960c: 5, 18, 27, 97, 105, 129, 160, 170, 172, 174, 177-80, 197, 264, Figs. 87, 

 123. 



S. bogorovi was found in 1958, during a cruise of R.V. Vityaz\ near the 

 east coast of New Zealand. Amongst five tubes three contained animals. This 

 species is named after Prof. V. G. Bogorov, organizer and leader of the 

 Pacific Ocean cruises of R.V. Vityaz\ The cyclindrical fore-part of the body is 



