288 PART II. SYSTEMATIC ACCOUNT 



species of Siboglinum. I have named this species Siboglinum concinnum (Lat. 

 concinnus — pleasing, shapely, elegant). 



The fore-part of the body is very long and cylindrical, with a length to 

 breadth ratio of 9 : 1. The protosoma is bounded behind by a distinct 

 annular groove, farther from the bridle than in S. subligatum sp. nov. 

 (p. 281). It is noticeably narrower than the mesosoma and rather short, 

 passing imperceptibly into the cephalic lobe in front. The latter is very small, 

 conical and pointed at the tip. The tentacle is attached rather nearer to the 

 hind end of the protosoma than to the tip of the cephalic lobe (Fig. ЕЕ 133Д 

 В). It is thin and moderately long, and sparsely furnished with pinnules 

 (175/x long) arranged in one row. The proximal part of the tentacle lacks 

 pinnules. A rather thick transparent cuticle can be seen, under the micro- 

 scope, covering the tentacle (Fig. EE133C). 



The bridle is situated near the front edge of the mesosoma. Its clear 

 transparent but comparatively thick keels lie on slightly protuberant ridges. 

 It is remarkable that the ventral ends of the keels are no thicker than the 

 rest; there is a small gap between them. The pair of ventral glandular patches 

 in front of the bridle look like low pear-shaped cushions, separated in the 

 mid-line only by a narrow longitudinal furrow. Behind the bridle are the 

 whitish longitudinal glandular ribbons of the mesosoma. They are rather 

 broad and begin on the lateral surfaces of the body just behind the ridges of 

 the bridle, running at first parallel to the latter onto the ventral side, then 

 extending backwards to the hind end of the mesosoma. At the very hind 

 end each ribbon makes a short bend on the ventral side (Fig. ЕЕ133Д B, 

 D). The boundary between the mesosoma and metasoma has no waist but is 

 a simple annular groove. 



The dorsal ciliated band of the metasoma is well developed. The ventral 

 sulcus is narrow. The metameric papillae are rounded and densely packed 

 together. The very anterior ones are a little larger, and towards the hind end 

 of the metameric section they become, as usual, a little larger once more. 

 There are about 70 pairs. A longitudinal band of glandular cells containing a 

 granular secretion runs along the external side of the bases of the papillae 

 on each side. In reflected light these bands appear light and, in transmitted 

 light, opaque (Fig. EE133Z)). 



The rest of the body is unknown. 



The broken fragment of the animal is 32 mm long, of which the tentacle 

 accounts for 6-9 mm, the fore-part of the body 2-1 mm and the metameric 

 section of the trunk 9 mm. The mesosoma is с 0-2 mm in diameter. 



The tube of S. concinnum is very like that of S. subligatum. Its surface is 



