SIBOGLINUM MICROCEPHALUM 229 



of the anterior section. At its very base the tentacle is a little swollen, but 

 this may well be an artefact. The tentacle itself is very long and slender and 

 devoid of pinnules (Fig. 116C). The protosoma is the same diameter as the 

 mesosoma. The very delicate crests or keels of the bridle are fused together 

 ventrally but do not quite meet dorsally, and the ridges of the bridle are 

 almost imperceptible. Behind the bridle is a glandular girdle, widely in- 

 terrupted on the dorsal side. The hind end of the mesosoma is curved and 

 notched in the mid-ventral line (Fig. 116у4, 2?, С). 



The comparatively large, round, metameric papillae number about 70-80 

 pairs. The ventral sulcus between them is rather broad, unlike the dorsal 

 ciliated band which begins a short distance from the front of the metasoma 

 (Fig. 1162?). The three girdles are all placed close together; the first two are 

 interrupted both dorsally and ventrally, but the last only ventrally (Fig. 

 116Z), E). The elongated oval toothed platelets, arranged in one row, have a 

 noticeable waist in the middle. The front end is a little narrower than the 

 back (Fig. 1167 7 ), and the front and back groups of teeth are separated by a 

 considerable naked area. While the anterior teeth are relatively few they are 

 well developed. The platelets are yellowish and 11-12/n long, with just a few 

 as short as 10/x; most of them are about 3/x broad. The very long and slender 

 postannular part of the trunk (Fig. 1 \1A) bears well-differentiated metameric 

 dorsal shields, shaped like cottage loaves (Fig. 116G). On the ventral side 

 opposite each shield lies a conical papilla with a small transparent cuticular 

 thickening on the tip (Fig. 116G, H). 



The only specimen is a male, to judge by the rather large anterior papillae 

 of the metameric part of the preannular region, but there is no sign of 

 spermatophores. 



The tentacle is 14 mm long, the fore-part of the body is 2-3 mm long and 

 0-18 mm broad; the preannular part of the trunk is 9-5 mm long, and the 

 postannular part 21 mm; the overall length including the tentacle is с 57 mm. 



The front part of the unsegmented tube is very soft, filmy, transparent and 

 limp (Fig. 1172?), then, in the walls of the tube, yellowish transverse fibres 

 begin to make an appearance (Fig. 117C). Farther back these form local 

 condensations or agglomerations, thus giving rise to muddy brown, fibrous 

 rings (Fig. 1172)), while between them the walls of the tube remain com- 

 pletely transparent. The rings are half as long as the diameter of the tube, 

 and the clear intervals between them are the same length, but towards the 

 hind end of the tube the rings become shorter and the intervals considerably 

 longer (Fig. 117£). The tube is 118 mm long and 0-19 mm in diameter near 

 the front end. 



