290 PART II. SYSTEMATIC ACCOUNT 



smooth and lustrous, its colour just perceptibly yellowish. The limp part 

 of the tube lacks wrinkles, but in the anterior part of the tube there are fine 

 circular ridges overlying superficial fibres. In the middle part, the tube is 

 thick-walled (30/x) and rather tough. The rings are more or less regular, 

 rather long and light greyish-brown. The one incomplete tube which we 

 possess is 80 mm long and 0-3 mm in diameter near the front end. 



Amongst the related "ribbon-bearing" or "taeniaphorous" species, 

 S. continuum is nearest to S. taeniaphorum and S. atlanticum, with which it 

 is linked by the possession of a single row of pinnules. It is distinguished 

 from these two species, however, by the pear-shaped outline of the glandular 

 areas of the mesosoma and particularly by the unthickened ventral ends of 

 the keels of the bridle. 



It is interesting to compare the longitudinal glandular ribbons of mesosoma 

 of these three species. In S. atlanticum they are clearly chopped up into 

 metameric sections which thus represent discrete areas of gland cells. In 

 S. taeniaphorum the ribbons present only traces of metamerism (and some- 

 times do not reach the hind end of the mesosoma). Finally, in S. continuum 

 they are continuous and homogeneous. If we bring the other taeniaphorous 

 species into the comparison as well, we may note that in S. subligatum sp. nov. 

 the longitudinal ribbons of the mesosoma are also homogeneous, and in 

 S. arabicum sp. nov. they broaden out at the hind end and break up into 

 small separate parts (isolated cells even) and do not reach the hind end of the 

 mesosoma. 



Material: one tube with front half of an animal. 



Locality: Vityaz 1 station 4680 (31st cruise): Indian Ocean near the coast 

 of East Africa to the east of Mafia Island, near Zanzibar. 



Depth: 802 m.] 



[32. Siboglinum arabicum sp. nov. Ivanov (Fig. FF133) 



Amongst the washings from a muddy bottom, brought up with bottom- 

 sampler or grab from a depth of 2385 m in the Arabian Sea at the mouth of 

 the Gulf of Aden in April 1960 (31st cruise of R.V Vityaz 1 ) I found one 

 transparent tube of Siboglinum. It contained an incomplete animal belonging 

 to the group of species possessing a pair of glandular mesosomal ribbons, but 

 it was clearly distinguished from all the known "taeniaphorous" or "ribbon- 

 bearing" species. 



The fore-part of the body of S. arabicum is cylindrical and eight and half 

 times as long as broad (Fig. FF133.4). The distance from the front end to 

 the bridle is half that from the bridle to the hind end of the fore-part. No 



