KEY, ORDERS, FAMILIES AND GENERA 153 



16 (15) The base of the tentacular crown is in the form of a circle. The cuticular 



plaques of the anterior papillae are kidney-shaped, with hoop-shaped 

 front edges. There are more than 100 pairs of metameric papillae. The 

 toothed platelets of the girdles lie in 3-4 rows. The tube is not ringed. 



2. Genus Cyclobrachia (p. 365). 



17 (14) Tentacles 2-4. The keels of the bridle consist of an axis, to which, from 



behind on the ventral side, are attached cuticular rodlets. 



3. Genus Diplobrachia (p. 370). 



18 (13) The protosoma is not divided from the mesosoma. The anterior meta- 



meric papillae lack cuticular plaques. 



19 (20) Two tentacles. The mesosoma is not divided from the metasoma. The 



tube is ringless, unsegmented, transparent, colourless or yellow and has 

 very thick rough walls. 7. Genus Sclerolinum (p. 418). 



20 (19) More than 10 tentacles. The mesosoma is clearly divided from the 



metasoma. The ringless tube is segmented, opaque and white, with 

 smooth walls. 4. Genus Zenkevitchiana (p. 388). 



21 (12) Tentacles not less than 18. The cephalic lobe is divided from the proto- 



soma by a pretentacular groove, or at least in some measure (in individuals 

 with the body extended) the two are sharply distinguished by the colour 

 and character of the integument. 



22 (23) The mesosoma in front of the bridle is ringed with transverse grooves and 



lacks wing-shaped cutaneous folds. Tentacles 18-70 or more. Each 

 papilla bears a single cuticular plaque. 



5. Genus Polybrachia (p. 393). 



23 (22) The mesosoma in front of the girdle is not ringed and possesses wing- 



shaped cutaneous folds. Tentacles 78-268. Some papillae in the non- 

 metameric part of the trunk bear several plaques each. 



6. Genus Galathealinum (p. 403). 



24 (11) Each tentacle adheres to the next. The cuticular plaques in the anterior 



part of the trunk lie on pulvilli, situated on the papillae. The mouth of the 

 tube is stiff and funnel-shaped. 



25 (26) Tentacles 10-31, fused into a hollow cylinder. The cuticular plaques on 



the front part of the trunk are shaped like horseshoes. 



II. Family Lamellisabellidae (p. 421). 



1. Genus Lamellisabella (p. 421). 



26 (25) Tentacles 39-223, fused into a tentacular plate which is rolled up into a 



spiral. Cuticular plaques in the front part of the trunk shaped like 

 brackets or hoops. 



III. Family Spirobrachiidae (p. 445). 



/. Genus Spirobrachia (p. 445). 



