322 PART II. SYSTEMATIC ACCOUNT 



The tentacle is 12-2 mm long, the fore-part of the body 0-8 mm, with a 

 greatest breadth of 0-25 mm. The metameric part of the trunk is 3-5 mm 

 long, the nonmetameric 8-5 mm and the postannular region 10-2 mm. The 

 overall length of the body, including the tentacle, is с 37 mm. As we have 

 seen, our specimen appears to be a young animal, and no sexual products 

 have been seen. 



The tube is very soft, colourless, thin-walled and structureless. Its whole 

 front half is flimsy. It is 94 mm long with an anterior diameter of c. 0-3 mm. 



S. sergeevi recalls 5. zanzibaricum sp. nov., but it is distinguished from 

 it by the presence of a sharply defined boundary between the protosoma 

 and mesosoma, the absence of pinnules, the dorsal separation of the keels 

 of the bridle, the underdeveloped anterior metameric papillae and the 

 structureless tube. 



Material : one tube with an entire animal. 



Locality: Vitya£ station 4492 (31st cruise): the southern part of the 

 Ceram Sea to the north of the Island of Bum. 



Substratum: grey-green clayey mud. 



Depth: 4774 m.] 



[39. Siboglinum lacteum sp. nov. E. C. Southward (Fig. YX133, PI. IV). 



One specimen of this species has been collected ; it was fortunately com- 

 plete and in good condition and was photographed while alive (see Plate IV). 



The animal is an immature female about 50 mm long but the coiling of 

 the posterior part of the body made exact measurement difficult. Fragments 

 of the tentacle are present, having a diameter of 50/x and bearing one semi- 

 double row of pinnules (Fig. YX133.5), each 50 to 80/x long. 



The fore-part is 2-4 mm long and 0-25 mm wide, without any obvious 

 transverse groove between proto- and mesosoma. The conical cephalic lobe 

 is rather small and sharply pointed (Fig. YX133.£, F). The ventral surface is 

 transversely grooved in front of the tentacle base, but this groove could be 

 an effect of contraction rather than a permanent feature of the species. 

 Behind the tentacle two ridges run alongside the mid-ventral furrow to the 

 point of the bridle and there is a slight notch in each a little before the bridle, 

 which may represent the groove between proto- and mesosoma. The mid- 

 ventral furrow continues a short way behind the bridle. The keels of the 

 bridle lie on a slight ridge, almost touching one another on the ventral side 

 but well separated dorsally (Fig. YX133D, E). In front of the bridle there are 

 two white patches of epidermal glands, and behind the bridle two ribbons 

 of the same glands extend back almost to the end of the mesosoma (Fig. 



