SIBOGLINUM SILONE 295 



consisting of the greater part of the body, besides five small scraps of tubes 

 containing parts of animals. I have named this new species Siboglinum silone 

 from its most characteristic feature — the broad flattened cephalic lobe (Lat. 

 silonis — flat-nosed, pug-nosed). 



The fore-part of the body is long and cylindrical and the protosoma is 

 clearly delimited. Its length to breadth ratio is usually 10 or 11 : 1 (Figs. 

 GG133, НН133Л, B), but in one specimen it was only 7:1. 



The short protosoma is considerably narrower than the mesosoma, and 

 bears a sharp post-tentacular groove (Fig. НН133у4-С). The cephalic lobe, 

 limited behind by a clear pretentacular groove, has an extraordinary shape. 

 It is dorso-ventrally flattened, very broad and leaf-shaped. It hardly tapers 

 to a proper tip and is sometimes even disc-like. In many individuals it is as 

 broad as long and exceeds twice the diameter of the protosoma. The epi- 

 dermis, particularly on the lateral expansions of the cephalic lobe, consists 

 of very tall large cells of a glandular nature (Fig. HH133). The tentacle is 

 long, but when it is contracted its proximal half is thickened (Figs. GG133, 

 HH1335-Z)). The delicate pinnules, 150-350/x long (obviously they can 

 expand and contract), are arranged in two dense rows along the whole length 

 of the tentacle (Figs. GG133, JJ133v4); but in a few individuals the proximal 

 part of the tentacle has no pinnules (Fig. НН133Л-С). The zone of formation 

 of the pinnules lies on the ventral surface of the tentacle to the left at its very 

 base (Fig. HH133Z)). Pinnule rudiments and small pinnules are arranged at 

 first in two parallel bands each formed of three dense parallel rows (Fig. 

 JJ 1 3 3 Л ) . Then, as the pinnules grow longer and differentiate, each band 

 opens out into a single longitudinal row (Fig. HH133D). The afferent and 

 efferent capillaries are particularly visible in this species. 



The anterior border of the mesosoma is an annular groove which runs 

 straight across the ventral side and runs forward in an arch on the dorsal 

 side (Fig. HH1332?). The bridle is found in the front part of the mesosoma. 

 Its keels are yellowish, their ventral ends fuse and their dorsal ends are 

 separated by a small gap (Fig. HH133). Behind the bridle the epidermis of 

 the mesosoma forms a rather large glandular area — a kind of broad glandular 

 girdle, interrupted or almost interrupted on the dorsal side (Fig. HH133). 

 The rest of the mesosoma has no outstanding peculiarities. In the coelom 

 of the mesosoma, behind the bridle, there are numerous small round flask- 

 shaped glands. The boundary between the mesosoma and metasoma is a 

 simple groove (Fig. НН133Д B). In the male a pair of large rounded genital 

 papillae lie on the ventral side in this region. 



The anterior part of the preannular region — the metameric section of the 



