178 PART II. SYSTEMATIC ACCOUNT 



19 (18) The post-tentacular groove is visible only on the ventral side. The 



pinnules are twice as long as the tentacle is wide. The keels of the 

 bridle are colourless. The two girdles are a long way apart and 

 the toothed platelets are 12-15/x long. The postannular papillae 

 bear bent rod-like cuticular plaques. 1. S. weberi (p. 181). 



20 (17) There is no post-tentacular groove. The toothed platelets are 



arranged in two or three rows in each of the two closely adjacent 

 girdles. 



21 (22) The groove between the protosoma and the mesosoma is simple. 



A prominent glandular girdle, broken on the ventral side, lies 

 behind the bridle. The keels of the bridle are thick and black. The 

 cephalic lobe is triangular and flattened. There are about ten 

 conical papillae in the zone of thickened papillae, arranged in a 

 single row and each bearing a bow-shaped cuticular plaque. The 

 tube has regular whitish or slightly muddy rings. 



8. S. cinctutum (p. 207). 



22 (21) The groove between the protosoma and the mesosoma curves 



strongly backwards on the dorsal side. There is no bulging 

 glandular girdle behind the bridle. The keels of the bridle are fine 

 and brownish. The cephalic lobe is conical. There are five papillae 

 in the zone of thickened papillae, arranged in a single row and 

 lacking cuticular plaques. The tube has very regular brown rings. 



10. S. caulleryi (p. 216). 



23 (8) Pinnules are absent. 



24 (25) The distance from the tip of the cepahlic lobe to the base of the 



tentacle is one fifth of that from the tip of the cephalic lobe to the 

 bridle. The toothed platelets, 10-13/x long, are arranged in one or 

 two rows. The unsegmented fibrous tube has regular short yellow- 

 ish or brownish rings. 14. S. meridiale (p. 231). 



25 (24) The distance from the tip of the cephalic lobe to the base of the ten- 



tacle is a half to a third of that from the tip of the lobe to the bridle. 



26 (35) There is an incomplete glandular girdle behind the bridle. 



27 (34) There are three girdles of toothed platelets, at least in some 



individuals. 



28 (29) The two anterior girdles of toothed platelets lie at a considerable 



distance from the hindmost. The toothed platelets measure 8-10/x 

 long. The keels of the bridle lie on brownish cuticular folds, crossed 

 by dark transverse rodlets. The unsegmented tube is fibrous, with 

 split, brown rings. 17. S. tenue (p. 238). 



