KEY FOR THE IDENTIFICATION FROM TUBES 457 



13 (12) The tube is unsegmented. 



14 (21) The rings are homogeneous. 



15 (18) In the hind part of the tube the rings become double or triple. 



16 (17) Side by side with double there are also triple rings. The diameter 



of the tube is 0-15-0-22 mm. Siboglinum hyperboreum (p. 236). 



17 (16) There are no triple rings. The diameter of the tube is 0-12 mm. 



Siboglinum pusillum (p. 221). 



18 (15) The rings in all parts of the tube are simple. 



19 (20) The rings are very short, never more than one quarter the diameter 



of the tube, yellow or brownish. The diameter reaches 0-34 mm. 



Siboglinum meridiale (p. 231). 



20 (19) The rings are long, but not longer than the diameter of the tube, 



coarse and dark brown or mud-coloured. The diameter of the tube 

 is 0-28-0-32 mm. Siboglinum japonicum (p. 200). 



21 (14) The rings in the hind part of the tube are inhomogeneous, i.e. 



consisting of irregular blotches of dark material with light irregular 

 spaces between them. In the hind part of the tube the rings dis- 

 integrate into two or three secondary rings. 



22 (23) For the greater part of the tube the rings are double. The length 



of the rings is much less than the diameter of the tube, which is 

 about 0-1 mm. Siboglinum tenue (p. 238). 



23 (22) Part of the tube has triple as well as double rings. The length of the 



rings is about equal to or only a little less than the diameter of the 

 tube, which is about 0-2 mm. Siboglinum bogorovi (p. 244). 



24 (7) The tube is not fibrous; if there are a few fibres then they are 



almost imperceptible. 



25 (30) The rings are white or just slightly brownish. The walls of the tube 



are stout and rather soft (easily cut with a sharp scalpel). The rings 

 are almost as long as or only a little less than the diameter of the 

 tube. 



26 (27) The diameter of the tube is 0-3-0-4 mm. 



Siboglinum cinctutum (p. 207). 



27 (26) The diameter of the tube is about 0-2 mm. 



28 (29) The rings are white, and in the front part of the tube just a little 



narrower in the middle. The diameter of the tube is slightly more 

 than 0-2 mm. Siboglinum vinculatum (p. 203). 



29 (28) The rings are just noticeably brownish, and not constricted in the 



middle. The diameter is a little less than 0-2 mm. 



Siboglinum frenigerum (p. 213). 



