180 PART II. SYSTEMATIC ACCOUNT 



spaced girdles. The unsegmented tube is not fibrous, but very limp 

 and transparent, with regular rings. 15. S. pellucidum (p. 233). 



38 (1) The keels of the bridle are divided on the ventral side. 



39 (40) The dorsal ends of the keels of the bridle merge into one another. 



There is no post-tentacular groove. The pinnules are disposed in a 

 single row. The spatulate toothed platelets, reaching 18/x in length, 

 are arranged in a single row in each of the three girdles, of which 

 the front two lie at a considerable distance from the hindmost. The 

 tube is transparent, with brownish rings. 



12. S. buccelliferum (p. 224). 



40 (39) The dorsal ends of the keels of the bridle are separated. 



41 (48) The mesosoma has more or less strongly developed glandular 



regions of integument. 



42 (47) Pinnules are present. 



43 (44) The pinnules are arranged in two rows and the tentacle is bi- 



pectinate. A pretentacular groove is present. The cephalic lobe is 

 rounded. The glandular structures of the mesosoma are represented 

 merely by a girdle, which is interrupted dorsally and ventrally and 

 lies close to the bridle. The metameric part of the metasoma lacks 

 lateral glandular tracts. The tube has very short irregular rings, 

 formed from split double rings. 5. S. plumosum (p. 197). 



44 (43) The pinnules are arranged in a single row and the tentacle is not 



bipectinate. A pretentacular groove is absent. The cephalic lobe is 

 conical. In front of the bridle there are two ventral glandular 

 regions, and behind it the lateral elements of the glandular girdle 

 are elongated on the ventral side into an obvious pair of glandular 

 tracts reaching backwards to the end of the mesosoma. There is a 

 long glandular tract also above the papillae of the metameric region 

 of the trunk on each side of the body. 



45 (46) The zone of thickened papillae has only three papillae arranged in 



a single row. There are two girdles of toothed platelets, and the 

 platelets measure 11-13^ long. The ventral papillae of the post- 

 annular region of the trunk have no cuticular plaques. The thick- 

 walled tube is segmented in front, with white semi-transparent 

 complete or broken rings, often anastomosing with one another. 



23. S. taeniaphorum (p. 257). 



46 (45) There are many papillae placed at random in the zone of thickened 



papillae. The toothed platelets, 14- 18/x long, are arranged in three 

 contiguous girdles. There are more than 130 pairs of papillae, in 



