176 PART II. SYSTEMATIC ACCOUNT 



Key for the identification of the species of the genus Siboglinum* 



* The following species have not been included in this partially revised version of the key given 

 in the Russian edition : 



Siboglinum cinctutum var subtile S. subligatum S. exile 



S. macrobrachium S. concinnum S. sumatrense 



S. debile S. arabicum S. zanzibaricum 



S. timorense S. silone S. sergeevi 



S. veleronis S. ceylonicum S. lacteum 



1 (38) The keels of the bridle are fused on the ventral side or come 



close together. 



2 (5) The keels of the bridle are fused on the dorsal side. 



3 (4) The keels of the bridle are very stout and their ventral ends merge 



imperceptibly into one another. The pinnules are arranged in a 

 single row. Behind the bridle there is a somewhat prominent 

 glandular ridge, interrupted dorsally and ventrally. There are 

 about 10 large papillae in the zone of thickened papillae, arranged 

 in a single row and bearing weak, round cuticular plaques. There 

 are two girdles of toothed platelets lying close together, with 

 platelets 10-1 1/x long. The tube is thick-walled, with slightly 

 brownish regular rings. 9. S.frenigerum (p. 213). 



4 (3) The keels of the bridle are moderately thick and their ventral ends 



are closely fused together. There is no prominent glandular girdle 

 behind the bridle. The pinnules are arranged in two rows. The 

 papillae are placed at random in the zone of thickening and bear 

 hoop-shaped cuticular plaques. There are two girdles of toothed 

 platelets lying close together, with platelets 11-13/x long. The tube 

 is thick-walled, with regular whitish rings. 



7. S. vinculatum (p. 203). 



5 (2) The keels of the bridle are not fused together on the dorsal side. 



6 (7) The protosoma has a pair of lateral protuberances at the base of the 



cephalic lobe. The very delicate keels of the bridle are crossed by 

 the finest of cuticular rodlets (use a microscope!). The toothed 

 platelets, 10-1 1/x long, are arranged in a single row in each of the 

 two adjacent girdles. The rings of the tube are irregular and brown 

 with reddish tints. 20. S. minutum (p. 248). 



7 (6) The protosoma lacks paired lateral protuberances at the base of the 



cephalic lobe. 



8 (23) Pinnules are present. 



9 (16) The pinnules form two rows. A pretentacular groove is present. 



